To have working BUG(), WARN(), ASSERT, run_in_exception_handler()
it is needed to enable GENERIC_BUG_FRAME.
Also, <xen/lib.h> is needed to be included for the reason that panic() and
printk() are used in common/bug.c and RISC-V fails if it is not included
with the following errors:
common/bug.c:69:9: error: implicit declaration of function 'printk'
[-Werror=implicit-function-declaration]
69 | printk("Xen WARN at %s%s:%d\n", prefix, filename,
lineno);
| ^~~~~~
common/bug.c:77:9: error: implicit declaration of function 'panic'
[-Werror=implicit-function-declaration]
77 | panic("Xen BUG at %s%s:%d\n", prefix, filename,
lineno);
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
Changes in V10:
- put 'select GENERIC_BUG_FRAME' in "Config RISCV".
- rework do_trap() to not fetch an instruction in case when the cause of trap
is BUG_insn.
- drop read_instr() and is_valid_bug_insn().
- update the commit message.
---
Changes in V9:
- Rebase on the top of current staging.
- use GENERIC_BUG_FRAME as now we have common code available.
- add xen/lib.h to bug.c to fix a compilation error around printk.
- update the commit message.
- update the code of read_instr() in traps.c
- fold two-s if into 1 in do_trap.
---
Changes in V8:
- remove Pointless initializer of id.
- make bug_frames[] array constant.
- remove cast_to_bug_frame(addr).
- rename is_valig_bugaddr to is_valid_bug_insn().
- add check that read_instr is used only on xen code
- update the commit message.
---
Changes in V7:
- move to this patch the definition of cast_to_bug_frame() from the previous patch.
- update the comment in bug.h.
- update the comment above do_bug_frame().
- fix code style.
- add comment to read_instr func.
- add space for bug_frames in lds.S.
---
Changes in V6:
- Avoid LINK_TO_LOAD() as bug.h functionality expected to be used
after MMU is enabled.
- Change early_printk() to printk()
---
Changes in V5:
- Remove "#include <xen/types.h>" from <asm/bug.h> as there is no any need in it anymore
- Update macros GET_INSN_LENGTH: remove UL and 'unsigned int len;' from it
- Remove " include <xen/bug.h>" from risc/setup.c. it is not needed in the current version of
the patch
- change an argument type from vaddr_t to uint32_t for is_valid_bugaddr and introduce read_instr() to
read instruction properly as the length of qinstruction can be either 32 or 16 bits.
- Code style fixes
- update the comments before do_bug_frame() in riscv/trap.c
- Refactor is_valid_bugaddr() function.
- introduce macros cast_to_bug_frame(addr) to hide casts.
- use LINK_TO_LOAD() for addresses which are linker time relative.
---
Changes in V4:
- Updates in RISC-V's <asm/bug.h>:
* Add explanatory comment about why there is only defined for 32-bits length
instructions and 16/32-bits BUG_INSN_{16,32}.
* Change 'unsigned long' to 'unsigned int' inside GET_INSN_LENGTH().
* Update declaration of is_valid_bugaddr(): switch return type from int to bool
and the argument from 'unsigned int' to 'vaddr'.
- Updates in RISC-V's traps.c:
* replace /xen and /asm includes
* update definition of is_valid_bugaddr():switch return type from int to bool
and the argument from 'unsigned int' to 'vaddr'. Code style inside function
was updated too.
* do_bug_frame() refactoring:
* local variables start and bug became 'const struct bug_frame'
* bug_frames[] array became 'static const struct bug_frame[] = ...'
* remove all casts
* remove unneeded comments and add an explanatory comment that the do_bug_frame()
will be switched to a generic one.
* do_trap() refactoring:
* read 16-bits value instead of 32-bits as compressed instruction can
be used and it might happen than only 16-bits may be accessible.
* code style updates
* re-use instr variable instead of re-reading instruction.
- Updates in setup.c:
* add blank line between xen/ and asm/ includes.
---
Changes in V3:
- Rebase the patch "xen/riscv: introduce an implementation of macros
from <asm/bug.h>" on top of patch series [introduce generic implementation
of macros from bug.h]
---
Changes in V2:
- Remove __ in define namings
- Update run_in_exception_handler() with
register void *fn_ asm(__stringify(BUG_FN_REG)) = (fn);
- Remove bug_instr_t type and change it's usage to uint32_t
---
xen/arch/riscv/Kconfig | 1 +
xen/arch/riscv/traps.c | 25 ++++++++++++++++++++++++-
xen/common/bug.c | 1 +
3 files changed, 26 insertions(+), 1 deletion(-)
diff --git a/xen/arch/riscv/Kconfig b/xen/arch/riscv/Kconfig
index b4b354a778..f531e96657 100644
--- a/xen/arch/riscv/Kconfig
+++ b/xen/arch/riscv/Kconfig
@@ -1,6 +1,7 @@
config RISCV
def_bool y
select FUNCTION_ALIGNMENT_16B
+ select GENERIC_BUG_FRAME
config RISCV_64
def_bool y
diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
index cb18b30ff2..e39603dc95 100644
--- a/xen/arch/riscv/traps.c
+++ b/xen/arch/riscv/traps.c
@@ -5,6 +5,7 @@
* RISC-V Trap handlers
*/
+#include <xen/bug.h>
#include <xen/lib.h>
#include <xen/sched.h>
@@ -103,7 +104,29 @@ static void do_unexpected_trap(const struct cpu_user_regs *regs)
void do_trap(struct cpu_user_regs *cpu_regs)
{
- do_unexpected_trap(cpu_regs);
+ register_t pc = cpu_regs->sepc;
+ unsigned long cause = csr_read(CSR_SCAUSE);
+
+ switch ( cause )
+ {
+ case CAUSE_BREAKPOINT:
+ if ( do_bug_frame(cpu_regs, pc) >= 0 )
+ {
+ if ( !pc ||
+ !(is_kernel_text(pc + 1) || is_kernel_inittext(pc + 1)) )
+ {
+ printk("Something wrong with PC: 0x%lx\n", pc);
+ die();
+ }
+
+ cpu_regs->sepc += GET_INSN_LENGTH(*(uint16_t *)pc);
+ return;
+ }
+
+ break;
+ default:
+ do_unexpected_trap(cpu_regs);
+ }
}
void vcpu_show_execution_state(struct vcpu *v)
diff --git a/xen/common/bug.c b/xen/common/bug.c
index b7c5d8fd4d..75cb35fcfa 100644
--- a/xen/common/bug.c
+++ b/xen/common/bug.c
@@ -1,6 +1,7 @@
#include <xen/bug.h>
#include <xen/errno.h>
#include <xen/kernel.h>
+#include <xen/lib.h>
#include <xen/livepatch.h>
#include <xen/string.h>
#include <xen/types.h>
--
2.45.2On 12.07.2024 18:18, Oleksii Kurochko wrote:
> To have working BUG(), WARN(), ASSERT, run_in_exception_handler()
> it is needed to enable GENERIC_BUG_FRAME.
>
> Also, <xen/lib.h> is needed to be included for the reason that panic() and
> printk() are used in common/bug.c and RISC-V fails if it is not included
> with the following errors:
> common/bug.c:69:9: error: implicit declaration of function 'printk'
> [-Werror=implicit-function-declaration]
> 69 | printk("Xen WARN at %s%s:%d\n", prefix, filename,
> lineno);
> | ^~~~~~
> common/bug.c:77:9: error: implicit declaration of function 'panic'
> [-Werror=implicit-function-declaration]
> 77 | panic("Xen BUG at %s%s:%d\n", prefix, filename,
> lineno);
I don't think the diagnostics themselves are needed here.
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> ---
> Changes in V10:
> - put 'select GENERIC_BUG_FRAME' in "Config RISCV".
> - rework do_trap() to not fetch an instruction in case when the cause of trap
> is BUG_insn.
It's BUG_insn here, but then ...
> @@ -103,7 +104,29 @@ static void do_unexpected_trap(const struct cpu_user_regs *regs)
>
> void do_trap(struct cpu_user_regs *cpu_regs)
> {
> - do_unexpected_trap(cpu_regs);
> + register_t pc = cpu_regs->sepc;
> + unsigned long cause = csr_read(CSR_SCAUSE);
> +
> + switch ( cause )
> + {
> + case CAUSE_BREAKPOINT:
... BREAKPOINT here? Generally I'd deem something named "breakpoint" as
debugging related (and hence continuable). I'd have expected
CAUSE_ILLEGAL_INSTRUCTION here, but likely I'm missing something.
> + if ( do_bug_frame(cpu_regs, pc) >= 0 )
> + {
> + if ( !pc ||
In how far does this really need special casing? Isn't that case covered by
> + !(is_kernel_text(pc + 1) || is_kernel_inittext(pc + 1)) )
... these checks anyway? And btw, why the "+ 1" in both function arguments?
> + {
> + printk("Something wrong with PC: 0x%lx\n", pc);
Nit: %#lx please in situations like this.
> + die();
> + }
> +
> + cpu_regs->sepc += GET_INSN_LENGTH(*(uint16_t *)pc);
> + return;
This isn't needed, is it? You'd return anyway by ...
> + }
> +
> + break;
.... going through here to ...
> + default:
> + do_unexpected_trap(cpu_regs);
> + }
> }
... here.
Two further nits for the default case: Please have a break statement
there as well, and please have a blank line immediately up from it.
Jan
On Mon, 2024-07-22 at 13:02 +0200, Jan Beulich wrote:
> On 12.07.2024 18:18, Oleksii Kurochko wrote:
> > To have working BUG(), WARN(), ASSERT, run_in_exception_handler()
> > it is needed to enable GENERIC_BUG_FRAME.
> >
> > Also, <xen/lib.h> is needed to be included for the reason that
> > panic() and
> > printk() are used in common/bug.c and RISC-V fails if it is not
> > included
> > with the following errors:
> > common/bug.c:69:9: error: implicit declaration of function
> > 'printk'
> > [-Werror=implicit-function-declaration]
> > 69 | printk("Xen WARN at %s%s:%d\n", prefix,
> > filename,
> > lineno);
> > | ^~~~~~
> > common/bug.c:77:9: error: implicit declaration of function
> > 'panic'
> > [-Werror=implicit-function-declaration]
> > 77 | panic("Xen BUG at %s%s:%d\n", prefix, filename,
> > lineno);
>
> I don't think the diagnostics themselves are needed here.
>
> > Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> > ---
> > Changes in V10:
> > - put 'select GENERIC_BUG_FRAME' in "Config RISCV".
> > - rework do_trap() to not fetch an instruction in case when the
> > cause of trap
> > is BUG_insn.
>
> It's BUG_insn here, but then ...
>
> > @@ -103,7 +104,29 @@ static void do_unexpected_trap(const struct
> > cpu_user_regs *regs)
> >
> > void do_trap(struct cpu_user_regs *cpu_regs)
> > {
> > - do_unexpected_trap(cpu_regs);
> > + register_t pc = cpu_regs->sepc;
> > + unsigned long cause = csr_read(CSR_SCAUSE);
> > +
> > + switch ( cause )
> > + {
> > + case CAUSE_BREAKPOINT:
>
> ... BREAKPOINT here? Generally I'd deem something named "breakpoint"
> as
> debugging related (and hence continuable). I'd have expected
> CAUSE_ILLEGAL_INSTRUCTION here, but likely I'm missing something.
Agree, that is is confusing, but BUG_insn is defined as ebreak
instruction ( Linux kernel uses also ebreak ) and it generates
CAUSE_BREAKPOINT.
>
> > + if ( do_bug_frame(cpu_regs, pc) >= 0 )
> > + {
> > + if ( !pc ||
>
> In how far does this really need special casing? Isn't that case
> covered by
>
> > + !(is_kernel_text(pc + 1) || is_kernel_inittext(pc
> > + 1)) )
>
> ... these checks anyway?
Good point. We could drop it.
> And btw, why the "+ 1" in both function arguments?
There is no need for them anymore, just missed to drop +1.
~ Oleksii
>
> > + {
> > + printk("Something wrong with PC: 0x%lx\n", pc);
>
> Nit: %#lx please in situations like this.
>
> > + die();
> > + }
> > +
> > + cpu_regs->sepc += GET_INSN_LENGTH(*(uint16_t *)pc);
> > + return;
>
> This isn't needed, is it? You'd return anyway by ...
>
> > + }
> > +
> > + break;
>
> .... going through here to ...
>
> > + default:
> > + do_unexpected_trap(cpu_regs);
> > + }
> > }
>
> ... here.
>
> Two further nits for the default case: Please have a break statement
> there as well, and please have a blank line immediately up from it.
>
> Jan
On 22.07.2024 16:09, Oleksii wrote:
> On Mon, 2024-07-22 at 13:02 +0200, Jan Beulich wrote:
>> On 12.07.2024 18:18, Oleksii Kurochko wrote:
>>> ---
>>> Changes in V10:
>>> - put 'select GENERIC_BUG_FRAME' in "Config RISCV".
>>> - rework do_trap() to not fetch an instruction in case when the
>>> cause of trap
>>> is BUG_insn.
>>
>> It's BUG_insn here, but then ...
>>
>>> @@ -103,7 +104,29 @@ static void do_unexpected_trap(const struct
>>> cpu_user_regs *regs)
>>>
>>> void do_trap(struct cpu_user_regs *cpu_regs)
>>> {
>>> - do_unexpected_trap(cpu_regs);
>>> + register_t pc = cpu_regs->sepc;
>>> + unsigned long cause = csr_read(CSR_SCAUSE);
>>> +
>>> + switch ( cause )
>>> + {
>>> + case CAUSE_BREAKPOINT:
>>
>> ... BREAKPOINT here? Generally I'd deem something named "breakpoint"
>> as
>> debugging related (and hence continuable). I'd have expected
>> CAUSE_ILLEGAL_INSTRUCTION here, but likely I'm missing something.
> Agree, that is is confusing, but BUG_insn is defined as ebreak
> instruction ( Linux kernel uses also ebreak ) and it generates
> CAUSE_BREAKPOINT.
I'm curious: How do you / does a debugger tell a breakpoint set on
such an EBREAK insn (e.g. as a result of a use of WARN_ON()) from
the original, unmodified insn? If there's a breakpoint, you want
to forward to the debugger. Whereas if there's no breakpoint, you
want to process the WARN_ON() normally.
Jan
On Mon, 2024-07-22 at 17:32 +0200, Jan Beulich wrote:
> On 22.07.2024 16:09, Oleksii wrote:
> > On Mon, 2024-07-22 at 13:02 +0200, Jan Beulich wrote:
> > > On 12.07.2024 18:18, Oleksii Kurochko wrote:
> > > > ---
> > > > Changes in V10:
> > > > - put 'select GENERIC_BUG_FRAME' in "Config RISCV".
> > > > - rework do_trap() to not fetch an instruction in case when
> > > > the
> > > > cause of trap
> > > > is BUG_insn.
> > >
> > > It's BUG_insn here, but then ...
> > >
> > > > @@ -103,7 +104,29 @@ static void do_unexpected_trap(const
> > > > struct
> > > > cpu_user_regs *regs)
> > > >
> > > > void do_trap(struct cpu_user_regs *cpu_regs)
> > > > {
> > > > - do_unexpected_trap(cpu_regs);
> > > > + register_t pc = cpu_regs->sepc;
> > > > + unsigned long cause = csr_read(CSR_SCAUSE);
> > > > +
> > > > + switch ( cause )
> > > > + {
> > > > + case CAUSE_BREAKPOINT:
> > >
> > > ... BREAKPOINT here? Generally I'd deem something named
> > > "breakpoint"
> > > as
> > > debugging related (and hence continuable). I'd have expected
> > > CAUSE_ILLEGAL_INSTRUCTION here, but likely I'm missing something.
> > Agree, that is is confusing, but BUG_insn is defined as ebreak
> > instruction ( Linux kernel uses also ebreak ) and it generates
> > CAUSE_BREAKPOINT.
>
> I'm curious: How do you / does a debugger tell a breakpoint set on
> such an EBREAK insn (e.g. as a result of a use of WARN_ON()) from
> the original, unmodified insn? If there's a breakpoint, you want
> to forward to the debugger. Whereas if there's no breakpoint, you
> want to process the WARN_ON() normally.
I don't know details of debug spec but AFAIU ebreak triggers a debug
trap, which starts in debug mode and is then filtered by every mode as
it goes towards user-mode. So first GDB will handle this debug trap and
will check if this ebreak was set by him or not.
~ Oleksii
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