arch/x86/boot/cpuflags.c | 26 +++++++++----------------- arch/x86/boot/cpuflags.h | 6 +++++- 2 files changed, 14 insertions(+), 18 deletions(-)
The test for the changeabitily of AC and ID eflags is used to
distinguish between i386 and i486 processors (AC) and to test
for cpuid instruction support (ID).
Skip these tests on x86_64 processors as they always supports cpuid.
Also change the return type of has_eflag() to bool.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
arch/x86/boot/cpuflags.c | 26 +++++++++-----------------
arch/x86/boot/cpuflags.h | 6 +++++-
2 files changed, 14 insertions(+), 18 deletions(-)
diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index d75237ba7ce9..2150a016176f 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -29,40 +29,32 @@ static int has_fpu(void)
return fsw == 0 && (fcw & 0x103f) == 0x003f;
}
+#ifdef CONFIG_X86_32
/*
* For building the 16-bit code we want to explicitly specify 32-bit
* push/pop operations, rather than just saying 'pushf' or 'popf' and
- * letting the compiler choose. But this is also included from the
- * compressed/ directory where it may be 64-bit code, and thus needs
- * to be 'pushfq' or 'popfq' in that case.
+ * letting the compiler choose.
*/
-#ifdef __x86_64__
-#define PUSHF "pushfq"
-#define POPF "popfq"
-#else
-#define PUSHF "pushfl"
-#define POPF "popfl"
-#endif
-
-int has_eflag(unsigned long mask)
+bool has_eflag(unsigned long mask)
{
unsigned long f0, f1;
- asm volatile(PUSHF " \n\t"
- PUSHF " \n\t"
+ asm volatile("pushfl \n\t"
+ "pushfl \n\t"
"pop %0 \n\t"
"mov %0,%1 \n\t"
"xor %2,%1 \n\t"
"push %1 \n\t"
- POPF " \n\t"
- PUSHF " \n\t"
+ "popfl \n\t"
+ "pushfl \n\t"
"pop %1 \n\t"
- POPF
+ "popfl"
: "=&r" (f0), "=&r" (f1)
: "ri" (mask));
return !!((f0^f1) & mask);
}
+#endif
void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
{
diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
index fdcc2aa4c3c4..a398d9204ad0 100644
--- a/arch/x86/boot/cpuflags.h
+++ b/arch/x86/boot/cpuflags.h
@@ -15,7 +15,11 @@ struct cpu_features {
extern struct cpu_features cpu;
extern u32 cpu_vendor[3];
-int has_eflag(unsigned long mask);
+#ifdef CONFIG_X86_32
+bool has_eflag(unsigned long mask);
+#else
+static inline bool has_eflag(unsigned long mask) { return true; }
+#endif
void get_cpuflags(void);
void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
bool has_cpuflag(int flag);
--
2.48.1On March 7, 2025 1:10:03 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote:
>The test for the changeabitily of AC and ID eflags is used to
>distinguish between i386 and i486 processors (AC) and to test
>for cpuid instruction support (ID).
>
>Skip these tests on x86_64 processors as they always supports cpuid.
>
>Also change the return type of has_eflag() to bool.
>
>Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
>Cc: Thomas Gleixner <tglx@linutronix.de>
>Cc: Ingo Molnar <mingo@kernel.org>
>Cc: Borislav Petkov <bp@alien8.de>
>Cc: Dave Hansen <dave.hansen@linux.intel.com>
>Cc: "H. Peter Anvin" <hpa@zytor.com>
>---
> arch/x86/boot/cpuflags.c | 26 +++++++++-----------------
> arch/x86/boot/cpuflags.h | 6 +++++-
> 2 files changed, 14 insertions(+), 18 deletions(-)
>
>diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
>index d75237ba7ce9..2150a016176f 100644
>--- a/arch/x86/boot/cpuflags.c
>+++ b/arch/x86/boot/cpuflags.c
>@@ -29,40 +29,32 @@ static int has_fpu(void)
> return fsw == 0 && (fcw & 0x103f) == 0x003f;
> }
>
>+#ifdef CONFIG_X86_32
> /*
> * For building the 16-bit code we want to explicitly specify 32-bit
> * push/pop operations, rather than just saying 'pushf' or 'popf' and
>- * letting the compiler choose. But this is also included from the
>- * compressed/ directory where it may be 64-bit code, and thus needs
>- * to be 'pushfq' or 'popfq' in that case.
>+ * letting the compiler choose.
> */
>-#ifdef __x86_64__
>-#define PUSHF "pushfq"
>-#define POPF "popfq"
>-#else
>-#define PUSHF "pushfl"
>-#define POPF "popfl"
>-#endif
>-
>-int has_eflag(unsigned long mask)
>+bool has_eflag(unsigned long mask)
> {
> unsigned long f0, f1;
>
>- asm volatile(PUSHF " \n\t"
>- PUSHF " \n\t"
>+ asm volatile("pushfl \n\t"
>+ "pushfl \n\t"
> "pop %0 \n\t"
> "mov %0,%1 \n\t"
> "xor %2,%1 \n\t"
> "push %1 \n\t"
>- POPF " \n\t"
>- PUSHF " \n\t"
>+ "popfl \n\t"
>+ "pushfl \n\t"
> "pop %1 \n\t"
>- POPF
>+ "popfl"
> : "=&r" (f0), "=&r" (f1)
> : "ri" (mask));
>
> return !!((f0^f1) & mask);
> }
>+#endif
>
> void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
> {
>diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
>index fdcc2aa4c3c4..a398d9204ad0 100644
>--- a/arch/x86/boot/cpuflags.h
>+++ b/arch/x86/boot/cpuflags.h
>@@ -15,7 +15,11 @@ struct cpu_features {
> extern struct cpu_features cpu;
> extern u32 cpu_vendor[3];
>
>-int has_eflag(unsigned long mask);
>+#ifdef CONFIG_X86_32
>+bool has_eflag(unsigned long mask);
>+#else
>+static inline bool has_eflag(unsigned long mask) { return true; }
>+#endif
> void get_cpuflags(void);
> void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
> bool has_cpuflag(int flag);
PUSF et al → pushf
The -l and -q suffixes have been optional for a long time.
On Fri, Mar 7, 2025 at 12:58 PM H. Peter Anvin <hpa@zytor.com> wrote:
>
> On March 7, 2025 1:10:03 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote:
> >The test for the changeabitily of AC and ID eflags is used to
> >distinguish between i386 and i486 processors (AC) and to test
> >for cpuid instruction support (ID).
> >
> >Skip these tests on x86_64 processors as they always supports cpuid.
> >
> >Also change the return type of has_eflag() to bool.
> >
> >Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> >Cc: Thomas Gleixner <tglx@linutronix.de>
> >Cc: Ingo Molnar <mingo@kernel.org>
> >Cc: Borislav Petkov <bp@alien8.de>
> >Cc: Dave Hansen <dave.hansen@linux.intel.com>
> >Cc: "H. Peter Anvin" <hpa@zytor.com>
> >---
> > arch/x86/boot/cpuflags.c | 26 +++++++++-----------------
> > arch/x86/boot/cpuflags.h | 6 +++++-
> > 2 files changed, 14 insertions(+), 18 deletions(-)
> >
> >diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
> >index d75237ba7ce9..2150a016176f 100644
> >--- a/arch/x86/boot/cpuflags.c
> >+++ b/arch/x86/boot/cpuflags.c
> >@@ -29,40 +29,32 @@ static int has_fpu(void)
> > return fsw == 0 && (fcw & 0x103f) == 0x003f;
> > }
> >
> >+#ifdef CONFIG_X86_32
> > /*
> > * For building the 16-bit code we want to explicitly specify 32-bit
> > * push/pop operations, rather than just saying 'pushf' or 'popf' and
> >- * letting the compiler choose. But this is also included from the
> >- * compressed/ directory where it may be 64-bit code, and thus needs
> >- * to be 'pushfq' or 'popfq' in that case.
> >+ * letting the compiler choose.
> > */
> >-#ifdef __x86_64__
> >-#define PUSHF "pushfq"
> >-#define POPF "popfq"
> >-#else
> >-#define PUSHF "pushfl"
> >-#define POPF "popfl"
> >-#endif
> >-
> >-int has_eflag(unsigned long mask)
> >+bool has_eflag(unsigned long mask)
> > {
> > unsigned long f0, f1;
> >
> >- asm volatile(PUSHF " \n\t"
> >- PUSHF " \n\t"
> >+ asm volatile("pushfl \n\t"
> >+ "pushfl \n\t"
> > "pop %0 \n\t"
> > "mov %0,%1 \n\t"
> > "xor %2,%1 \n\t"
> > "push %1 \n\t"
> >- POPF " \n\t"
> >- PUSHF " \n\t"
> >+ "popfl \n\t"
> >+ "pushfl \n\t"
> > "pop %1 \n\t"
> >- POPF
> >+ "popfl"
> > : "=&r" (f0), "=&r" (f1)
> > : "ri" (mask));
> >
> > return !!((f0^f1) & mask);
> > }
> >+#endif
> >
> > void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
> > {
> >diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
> >index fdcc2aa4c3c4..a398d9204ad0 100644
> >--- a/arch/x86/boot/cpuflags.h
> >+++ b/arch/x86/boot/cpuflags.h
> >@@ -15,7 +15,11 @@ struct cpu_features {
> > extern struct cpu_features cpu;
> > extern u32 cpu_vendor[3];
> >
> >-int has_eflag(unsigned long mask);
> >+#ifdef CONFIG_X86_32
> >+bool has_eflag(unsigned long mask);
> >+#else
> >+static inline bool has_eflag(unsigned long mask) { return true; }
> >+#endif
> > void get_cpuflags(void);
> > void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
> > bool has_cpuflag(int flag);
>
> PUSF et al → pushf
>
> The -l and -q suffixes have been optional for a long time.
No, not in this case. Please see the comment:
/*
* For building the 16-bit code we want to explicitly specify 32-bit
* push/pop operations, rather than just saying 'pushf' or 'popf' and
* letting the compiler choose.
*/
We are building 16-bit code here, and we want PUSHFL, the one with
operand size prefix 0x66.
Please consider the following code:
.code16
pushf
pushfl
as -o push.o push.s
objdump -dr -Mdata16 push.o
0000000000000000 <.text>:
0: 9c pushf
1: 66 9c pushfl
Uros.
On March 7, 2025 4:15:42 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote:
>On Fri, Mar 7, 2025 at 12:58 PM H. Peter Anvin <hpa@zytor.com> wrote:
>>
>> On March 7, 2025 1:10:03 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote:
>> >The test for the changeabitily of AC and ID eflags is used to
>> >distinguish between i386 and i486 processors (AC) and to test
>> >for cpuid instruction support (ID).
>> >
>> >Skip these tests on x86_64 processors as they always supports cpuid.
>> >
>> >Also change the return type of has_eflag() to bool.
>> >
>> >Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
>> >Cc: Thomas Gleixner <tglx@linutronix.de>
>> >Cc: Ingo Molnar <mingo@kernel.org>
>> >Cc: Borislav Petkov <bp@alien8.de>
>> >Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> >Cc: "H. Peter Anvin" <hpa@zytor.com>
>> >---
>> > arch/x86/boot/cpuflags.c | 26 +++++++++-----------------
>> > arch/x86/boot/cpuflags.h | 6 +++++-
>> > 2 files changed, 14 insertions(+), 18 deletions(-)
>> >
>> >diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
>> >index d75237ba7ce9..2150a016176f 100644
>> >--- a/arch/x86/boot/cpuflags.c
>> >+++ b/arch/x86/boot/cpuflags.c
>> >@@ -29,40 +29,32 @@ static int has_fpu(void)
>> > return fsw == 0 && (fcw & 0x103f) == 0x003f;
>> > }
>> >
>> >+#ifdef CONFIG_X86_32
>> > /*
>> > * For building the 16-bit code we want to explicitly specify 32-bit
>> > * push/pop operations, rather than just saying 'pushf' or 'popf' and
>> >- * letting the compiler choose. But this is also included from the
>> >- * compressed/ directory where it may be 64-bit code, and thus needs
>> >- * to be 'pushfq' or 'popfq' in that case.
>> >+ * letting the compiler choose.
>> > */
>> >-#ifdef __x86_64__
>> >-#define PUSHF "pushfq"
>> >-#define POPF "popfq"
>> >-#else
>> >-#define PUSHF "pushfl"
>> >-#define POPF "popfl"
>> >-#endif
>> >-
>> >-int has_eflag(unsigned long mask)
>> >+bool has_eflag(unsigned long mask)
>> > {
>> > unsigned long f0, f1;
>> >
>> >- asm volatile(PUSHF " \n\t"
>> >- PUSHF " \n\t"
>> >+ asm volatile("pushfl \n\t"
>> >+ "pushfl \n\t"
>> > "pop %0 \n\t"
>> > "mov %0,%1 \n\t"
>> > "xor %2,%1 \n\t"
>> > "push %1 \n\t"
>> >- POPF " \n\t"
>> >- PUSHF " \n\t"
>> >+ "popfl \n\t"
>> >+ "pushfl \n\t"
>> > "pop %1 \n\t"
>> >- POPF
>> >+ "popfl"
>> > : "=&r" (f0), "=&r" (f1)
>> > : "ri" (mask));
>> >
>> > return !!((f0^f1) & mask);
>> > }
>> >+#endif
>> >
>> > void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
>> > {
>> >diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
>> >index fdcc2aa4c3c4..a398d9204ad0 100644
>> >--- a/arch/x86/boot/cpuflags.h
>> >+++ b/arch/x86/boot/cpuflags.h
>> >@@ -15,7 +15,11 @@ struct cpu_features {
>> > extern struct cpu_features cpu;
>> > extern u32 cpu_vendor[3];
>> >
>> >-int has_eflag(unsigned long mask);
>> >+#ifdef CONFIG_X86_32
>> >+bool has_eflag(unsigned long mask);
>> >+#else
>> >+static inline bool has_eflag(unsigned long mask) { return true; }
>> >+#endif
>> > void get_cpuflags(void);
>> > void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
>> > bool has_cpuflag(int flag);
>>
>> PUSF et al → pushf
>>
>> The -l and -q suffixes have been optional for a long time.
>
>No, not in this case. Please see the comment:
>
>/*
>* For building the 16-bit code we want to explicitly specify 32-bit
>* push/pop operations, rather than just saying 'pushf' or 'popf' and
>* letting the compiler choose.
>*/
>
>We are building 16-bit code here, and we want PUSHFL, the one with
>operand size prefix 0x66.
>
>Please consider the following code:
>
> .code16
> pushf
> pushfl
>
>as -o push.o push.s
>
>objdump -dr -Mdata16 push.o
>
>0000000000000000 <.text>:
> 0: 9c pushf
> 1: 66 9c pushfl
>
>Uros.
>
*plonk* I should have remembered (.code16gcc is different then .code16 though.) I wrote the damned things after all...
* H. Peter Anvin <hpa@zytor.com> wrote:
> On March 7, 2025 4:15:42 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote:
> >On Fri, Mar 7, 2025 at 12:58 PM H. Peter Anvin <hpa@zytor.com> wrote:
> >>
> >> On March 7, 2025 1:10:03 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote:
> >> >The test for the changeabitily of AC and ID eflags is used to
> >> >distinguish between i386 and i486 processors (AC) and to test
> >> >for cpuid instruction support (ID).
> >> >
> >> >Skip these tests on x86_64 processors as they always supports cpuid.
> >> >
> >> >Also change the return type of has_eflag() to bool.
> >> >
> >> >Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> >> >Cc: Thomas Gleixner <tglx@linutronix.de>
> >> >Cc: Ingo Molnar <mingo@kernel.org>
> >> >Cc: Borislav Petkov <bp@alien8.de>
> >> >Cc: Dave Hansen <dave.hansen@linux.intel.com>
> >> >Cc: "H. Peter Anvin" <hpa@zytor.com>
> >> >---
> >> > arch/x86/boot/cpuflags.c | 26 +++++++++-----------------
> >> > arch/x86/boot/cpuflags.h | 6 +++++-
> >> > 2 files changed, 14 insertions(+), 18 deletions(-)
> >> >
> >> >diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
> >> >index d75237ba7ce9..2150a016176f 100644
> >> >--- a/arch/x86/boot/cpuflags.c
> >> >+++ b/arch/x86/boot/cpuflags.c
> >> >@@ -29,40 +29,32 @@ static int has_fpu(void)
> >> > return fsw == 0 && (fcw & 0x103f) == 0x003f;
> >> > }
> >> >
> >> >+#ifdef CONFIG_X86_32
> >> > /*
> >> > * For building the 16-bit code we want to explicitly specify 32-bit
> >> > * push/pop operations, rather than just saying 'pushf' or 'popf' and
> >> >- * letting the compiler choose. But this is also included from the
> >> >- * compressed/ directory where it may be 64-bit code, and thus needs
> >> >- * to be 'pushfq' or 'popfq' in that case.
> >> >+ * letting the compiler choose.
> >> > */
> >> >-#ifdef __x86_64__
> >> >-#define PUSHF "pushfq"
> >> >-#define POPF "popfq"
> >> >-#else
> >> >-#define PUSHF "pushfl"
> >> >-#define POPF "popfl"
> >> >-#endif
> >> >-
> >> >-int has_eflag(unsigned long mask)
> >> >+bool has_eflag(unsigned long mask)
> >> > {
> >> > unsigned long f0, f1;
> >> >
> >> >- asm volatile(PUSHF " \n\t"
> >> >- PUSHF " \n\t"
> >> >+ asm volatile("pushfl \n\t"
> >> >+ "pushfl \n\t"
> >> > "pop %0 \n\t"
> >> > "mov %0,%1 \n\t"
> >> > "xor %2,%1 \n\t"
> >> > "push %1 \n\t"
> >> >- POPF " \n\t"
> >> >- PUSHF " \n\t"
> >> >+ "popfl \n\t"
> >> >+ "pushfl \n\t"
> >> > "pop %1 \n\t"
> >> >- POPF
> >> >+ "popfl"
> >> > : "=&r" (f0), "=&r" (f1)
> >> > : "ri" (mask));
> >> >
> >> > return !!((f0^f1) & mask);
> >> > }
> >> >+#endif
> >> >
> >> > void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
> >> > {
> >> >diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
> >> >index fdcc2aa4c3c4..a398d9204ad0 100644
> >> >--- a/arch/x86/boot/cpuflags.h
> >> >+++ b/arch/x86/boot/cpuflags.h
> >> >@@ -15,7 +15,11 @@ struct cpu_features {
> >> > extern struct cpu_features cpu;
> >> > extern u32 cpu_vendor[3];
> >> >
> >> >-int has_eflag(unsigned long mask);
> >> >+#ifdef CONFIG_X86_32
> >> >+bool has_eflag(unsigned long mask);
> >> >+#else
> >> >+static inline bool has_eflag(unsigned long mask) { return true; }
> >> >+#endif
> >> > void get_cpuflags(void);
> >> > void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
> >> > bool has_cpuflag(int flag);
> >>
> >> PUSF et al → pushf
> >>
> >> The -l and -q suffixes have been optional for a long time.
> >
> >No, not in this case. Please see the comment:
> >
> >/*
> >* For building the 16-bit code we want to explicitly specify 32-bit
> >* push/pop operations, rather than just saying 'pushf' or 'popf' and
> >* letting the compiler choose.
> >*/
> >
> >We are building 16-bit code here, and we want PUSHFL, the one with
> >operand size prefix 0x66.
> >
> >Please consider the following code:
> >
> > .code16
> > pushf
> > pushfl
> >
> >as -o push.o push.s
> >
> >objdump -dr -Mdata16 push.o
> >
> >0000000000000000 <.text>:
> > 0: 9c pushf
> > 1: 66 9c pushfl
> >
> >Uros.
> >
>
> *plonk* I should have remembered (.code16gcc is different then
> .code16 though.) I wrote the damned things after all...
So I'll read this as a tentative:
Acked-by: H. Peter Anvin <hpa@zytor.com>
Let me know if I'm not reading the room right. :-)
Ingo
On March 8, 2025 11:34:49 AM PST, Ingo Molnar <mingo@kernel.org> wrote:
>
>* H. Peter Anvin <hpa@zytor.com> wrote:
>
>> On March 7, 2025 4:15:42 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote:
>> >On Fri, Mar 7, 2025 at 12:58 PM H. Peter Anvin <hpa@zytor.com> wrote:
>> >>
>> >> On March 7, 2025 1:10:03 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote:
>> >> >The test for the changeabitily of AC and ID eflags is used to
>> >> >distinguish between i386 and i486 processors (AC) and to test
>> >> >for cpuid instruction support (ID).
>> >> >
>> >> >Skip these tests on x86_64 processors as they always supports cpuid.
>> >> >
>> >> >Also change the return type of has_eflag() to bool.
>> >> >
>> >> >Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
>> >> >Cc: Thomas Gleixner <tglx@linutronix.de>
>> >> >Cc: Ingo Molnar <mingo@kernel.org>
>> >> >Cc: Borislav Petkov <bp@alien8.de>
>> >> >Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> >> >Cc: "H. Peter Anvin" <hpa@zytor.com>
>> >> >---
>> >> > arch/x86/boot/cpuflags.c | 26 +++++++++-----------------
>> >> > arch/x86/boot/cpuflags.h | 6 +++++-
>> >> > 2 files changed, 14 insertions(+), 18 deletions(-)
>> >> >
>> >> >diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
>> >> >index d75237ba7ce9..2150a016176f 100644
>> >> >--- a/arch/x86/boot/cpuflags.c
>> >> >+++ b/arch/x86/boot/cpuflags.c
>> >> >@@ -29,40 +29,32 @@ static int has_fpu(void)
>> >> > return fsw == 0 && (fcw & 0x103f) == 0x003f;
>> >> > }
>> >> >
>> >> >+#ifdef CONFIG_X86_32
>> >> > /*
>> >> > * For building the 16-bit code we want to explicitly specify 32-bit
>> >> > * push/pop operations, rather than just saying 'pushf' or 'popf' and
>> >> >- * letting the compiler choose. But this is also included from the
>> >> >- * compressed/ directory where it may be 64-bit code, and thus needs
>> >> >- * to be 'pushfq' or 'popfq' in that case.
>> >> >+ * letting the compiler choose.
>> >> > */
>> >> >-#ifdef __x86_64__
>> >> >-#define PUSHF "pushfq"
>> >> >-#define POPF "popfq"
>> >> >-#else
>> >> >-#define PUSHF "pushfl"
>> >> >-#define POPF "popfl"
>> >> >-#endif
>> >> >-
>> >> >-int has_eflag(unsigned long mask)
>> >> >+bool has_eflag(unsigned long mask)
>> >> > {
>> >> > unsigned long f0, f1;
>> >> >
>> >> >- asm volatile(PUSHF " \n\t"
>> >> >- PUSHF " \n\t"
>> >> >+ asm volatile("pushfl \n\t"
>> >> >+ "pushfl \n\t"
>> >> > "pop %0 \n\t"
>> >> > "mov %0,%1 \n\t"
>> >> > "xor %2,%1 \n\t"
>> >> > "push %1 \n\t"
>> >> >- POPF " \n\t"
>> >> >- PUSHF " \n\t"
>> >> >+ "popfl \n\t"
>> >> >+ "pushfl \n\t"
>> >> > "pop %1 \n\t"
>> >> >- POPF
>> >> >+ "popfl"
>> >> > : "=&r" (f0), "=&r" (f1)
>> >> > : "ri" (mask));
>> >> >
>> >> > return !!((f0^f1) & mask);
>> >> > }
>> >> >+#endif
>> >> >
>> >> > void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
>> >> > {
>> >> >diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
>> >> >index fdcc2aa4c3c4..a398d9204ad0 100644
>> >> >--- a/arch/x86/boot/cpuflags.h
>> >> >+++ b/arch/x86/boot/cpuflags.h
>> >> >@@ -15,7 +15,11 @@ struct cpu_features {
>> >> > extern struct cpu_features cpu;
>> >> > extern u32 cpu_vendor[3];
>> >> >
>> >> >-int has_eflag(unsigned long mask);
>> >> >+#ifdef CONFIG_X86_32
>> >> >+bool has_eflag(unsigned long mask);
>> >> >+#else
>> >> >+static inline bool has_eflag(unsigned long mask) { return true; }
>> >> >+#endif
>> >> > void get_cpuflags(void);
>> >> > void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
>> >> > bool has_cpuflag(int flag);
>> >>
>> >> PUSF et al → pushf
>> >>
>> >> The -l and -q suffixes have been optional for a long time.
>> >
>> >No, not in this case. Please see the comment:
>> >
>> >/*
>> >* For building the 16-bit code we want to explicitly specify 32-bit
>> >* push/pop operations, rather than just saying 'pushf' or 'popf' and
>> >* letting the compiler choose.
>> >*/
>> >
>> >We are building 16-bit code here, and we want PUSHFL, the one with
>> >operand size prefix 0x66.
>> >
>> >Please consider the following code:
>> >
>> > .code16
>> > pushf
>> > pushfl
>> >
>> >as -o push.o push.s
>> >
>> >objdump -dr -Mdata16 push.o
>> >
>> >0000000000000000 <.text>:
>> > 0: 9c pushf
>> > 1: 66 9c pushfl
>> >
>> >Uros.
>> >
>>
>> *plonk* I should have remembered (.code16gcc is different then
>> .code16 though.) I wrote the damned things after all...
>
>So I'll read this as a tentative:
>
> Acked-by: H. Peter Anvin <hpa@zytor.com>
>
>Let me know if I'm not reading the room right. :-)
>
> Ingo
Indeed.
On Fri, Mar 7, 2025 at 2:13 PM H. Peter Anvin <hpa@zytor.com> wrote: > >> PUSF et al → pushf > >> > >> The -l and -q suffixes have been optional for a long time. > > > >No, not in this case. Please see the comment: > > > >/* > >* For building the 16-bit code we want to explicitly specify 32-bit > >* push/pop operations, rather than just saying 'pushf' or 'popf' and > >* letting the compiler choose. > >*/ > > > >We are building 16-bit code here, and we want PUSHFL, the one with > >operand size prefix 0x66. > > > >Please consider the following code: > > > > .code16 > > pushf > > pushfl > > > >as -o push.o push.s > > > >objdump -dr -Mdata16 push.o > > > >0000000000000000 <.text>: > > 0: 9c pushf > > 1: 66 9c pushfl > > > >Uros. > > > > *plonk* I should have remembered (.code16gcc is different then .code16 though.) I wrote the damned things after all... Please note that while "gcc -m16" emits .code16gcc, "clang -m16" emits .code16, so in the latter case we don't have ‘pushf’, and ‘popf’ instructions default to 32-bit size. So, the only solution is to decorate pushfl with operand size prefix in this specific case. Uros.
On March 7, 2025 5:45:42 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote: >On Fri, Mar 7, 2025 at 2:13 PM H. Peter Anvin <hpa@zytor.com> wrote: > >> >> PUSF et al → pushf >> >> >> >> The -l and -q suffixes have been optional for a long time. >> > >> >No, not in this case. Please see the comment: >> > >> >/* >> >* For building the 16-bit code we want to explicitly specify 32-bit >> >* push/pop operations, rather than just saying 'pushf' or 'popf' and >> >* letting the compiler choose. >> >*/ >> > >> >We are building 16-bit code here, and we want PUSHFL, the one with >> >operand size prefix 0x66. >> > >> >Please consider the following code: >> > >> > .code16 >> > pushf >> > pushfl >> > >> >as -o push.o push.s >> > >> >objdump -dr -Mdata16 push.o >> > >> >0000000000000000 <.text>: >> > 0: 9c pushf >> > 1: 66 9c pushfl >> > >> >Uros. >> > >> >> *plonk* I should have remembered (.code16gcc is different then .code16 though.) I wrote the damned things after all... > >Please note that while "gcc -m16" emits .code16gcc, "clang -m16" emits >.code16, so in the latter case we don't have ‘pushf’, and ‘popf’ >instructions default to 32-bit size. So, the only solution is to >decorate pushfl with operand size prefix in this specific case. > >Uros. > Can you please beat up the clang people who do gratuitously incompatible things like this?
On Fri, Mar 7, 2025 at 3:46 PM H. Peter Anvin <hpa@zytor.com> wrote: > > On March 7, 2025 5:45:42 AM PST, Uros Bizjak <ubizjak@gmail.com> wrote: > >On Fri, Mar 7, 2025 at 2:13 PM H. Peter Anvin <hpa@zytor.com> wrote: > > > >> >> PUSF et al → pushf > >> >> > >> >> The -l and -q suffixes have been optional for a long time. > >> > > >> >No, not in this case. Please see the comment: > >> > > >> >/* > >> >* For building the 16-bit code we want to explicitly specify 32-bit > >> >* push/pop operations, rather than just saying 'pushf' or 'popf' and > >> >* letting the compiler choose. > >> >*/ > >> > > >> >We are building 16-bit code here, and we want PUSHFL, the one with > >> >operand size prefix 0x66. > >> > > >> >Please consider the following code: > >> > > >> > .code16 > >> > pushf > >> > pushfl > >> > > >> >as -o push.o push.s > >> > > >> >objdump -dr -Mdata16 push.o > >> > > >> >0000000000000000 <.text>: > >> > 0: 9c pushf > >> > 1: 66 9c pushfl > >> > > >> >Uros. > >> > > >> > >> *plonk* I should have remembered (.code16gcc is different then .code16 though.) I wrote the damned things after all... > > > >Please note that while "gcc -m16" emits .code16gcc, "clang -m16" emits > >.code16, so in the latter case we don't have ‘pushf’, and ‘popf’ > >instructions default to 32-bit size. So, the only solution is to > >decorate pushfl with operand size prefix in this specific case. > > > >Uros. > > > > Can you please beat up the clang people who do gratuitously incompatible things like this? :) BTW: This patch is actually the implementation you requested at some previous discussion [1], but I took the approach similar to the definition of have_cpuid_p() in cpuid.h [2]. [1] https://lore.kernel.org/lkml/0A743606-067F-450C-85A5-55ECE4378E22@zytor.com/#t [2] https://elixir.bootlin.com/linux/v6.14-rc5/source/arch/x86/include/asm/cpuid.h#L32 Uros.
The following commit has been merged into the x86/boot branch of tip:
Commit-ID: 558fc8e1869ca6e1eb99a1e2b52f6c35424d4adf
Gitweb: https://git.kernel.org/tip/558fc8e1869ca6e1eb99a1e2b52f6c35424d4adf
Author: Uros Bizjak <ubizjak@gmail.com>
AuthorDate: Fri, 07 Mar 2025 10:10:03 +01:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Sat, 08 Mar 2025 20:36:26 +01:00
x86/boot: Do not test if AC and ID eflags are changeable on x86_64
The test for the changeabitily of AC and ID EFLAGS is used to
distinguish between i386 and i486 processors (AC) and to test
for CPUID instruction support (ID).
Skip these tests on x86_64 processors as they always supports CPUID.
Also change the return type of has_eflag() to bool.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20250307091022.181136-1-ubizjak@gmail.com
---
arch/x86/boot/cpuflags.c | 26 +++++++++-----------------
arch/x86/boot/cpuflags.h | 6 +++++-
2 files changed, 14 insertions(+), 18 deletions(-)
diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index d75237b..2150a01 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -29,40 +29,32 @@ static int has_fpu(void)
return fsw == 0 && (fcw & 0x103f) == 0x003f;
}
+#ifdef CONFIG_X86_32
/*
* For building the 16-bit code we want to explicitly specify 32-bit
* push/pop operations, rather than just saying 'pushf' or 'popf' and
- * letting the compiler choose. But this is also included from the
- * compressed/ directory where it may be 64-bit code, and thus needs
- * to be 'pushfq' or 'popfq' in that case.
+ * letting the compiler choose.
*/
-#ifdef __x86_64__
-#define PUSHF "pushfq"
-#define POPF "popfq"
-#else
-#define PUSHF "pushfl"
-#define POPF "popfl"
-#endif
-
-int has_eflag(unsigned long mask)
+bool has_eflag(unsigned long mask)
{
unsigned long f0, f1;
- asm volatile(PUSHF " \n\t"
- PUSHF " \n\t"
+ asm volatile("pushfl \n\t"
+ "pushfl \n\t"
"pop %0 \n\t"
"mov %0,%1 \n\t"
"xor %2,%1 \n\t"
"push %1 \n\t"
- POPF " \n\t"
- PUSHF " \n\t"
+ "popfl \n\t"
+ "pushfl \n\t"
"pop %1 \n\t"
- POPF
+ "popfl"
: "=&r" (f0), "=&r" (f1)
: "ri" (mask));
return !!((f0^f1) & mask);
}
+#endif
void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
{
diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
index fdcc2aa..a398d92 100644
--- a/arch/x86/boot/cpuflags.h
+++ b/arch/x86/boot/cpuflags.h
@@ -15,7 +15,11 @@ struct cpu_features {
extern struct cpu_features cpu;
extern u32 cpu_vendor[3];
-int has_eflag(unsigned long mask);
+#ifdef CONFIG_X86_32
+bool has_eflag(unsigned long mask);
+#else
+static inline bool has_eflag(unsigned long mask) { return true; }
+#endif
void get_cpuflags(void);
void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
bool has_cpuflag(int flag);© 2016 - 2026 Red Hat, Inc.