[PATCH v2] linux-user: limit check to HOST_LONG_BITS == 32

Alex Bennée posted 1 patch 1 week ago
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git fetch https://github.com/patchew-project/qemu tags/patchew/20200521135748.9859-1-alex.bennee@linaro.org
linux-user/elfload.c | 2 ++
1 file changed, 2 insertions(+)

[PATCH v2] linux-user: limit check to HOST_LONG_BITS == 32

Posted by Alex Bennée 1 week ago
Newer clangs rightly spot that you can never exceed the full address
space of 64 bit hosts with:

  linux-user/elfload.c:2076:41: error: result of comparison 'unsigned
  long' > 18446744073709551615 is always false
  [-Werror,-Wtautological-type-limit-compare]
  4685         if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
  4686             ~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
  4687 1 error generated.

So lets limit the check to 32 bit hosts only.

Fixes: ee94743034bf
Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v2
  - move inside else bracket
---
 linux-user/elfload.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 01a9323a637..de82eaf5420 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2073,12 +2073,14 @@ static void pgb_have_guest_base(const char *image_name, abi_ulong guest_loaddr,
             exit(EXIT_FAILURE);
         }
     } else {
+#if HOST_LONG_BITS == 32
         if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
             error_report("%s: requires more virtual address space "
                          "than the host can provide (0x%" PRIx64 ")",
                          image_name, (uint64_t)guest_hiaddr - guest_base);
             exit(EXIT_FAILURE);
         }
+#endif
     }
 
     /*
-- 
2.20.1


Re: [PATCH v2] linux-user: limit check to HOST_LONG_BITS == 32

Posted by Richard Henderson 1 week ago
On 5/21/20 6:57 AM, Alex Bennée wrote:
> Newer clangs rightly spot that you can never exceed the full address
> space of 64 bit hosts with:
> 
>   linux-user/elfload.c:2076:41: error: result of comparison 'unsigned
>   long' > 18446744073709551615 is always false
>   [-Werror,-Wtautological-type-limit-compare]
>   4685         if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
>   4686             ~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
>   4687 1 error generated.
> 
> So lets limit the check to 32 bit hosts only.
> 
> Fixes: ee94743034bf
> Reported-by: Thomas Huth <thuth@redhat.com>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> 
> ---

I say again that I'd prefer that we disable this warning.


r~

Re: [PATCH v2] linux-user: limit check to HOST_LONG_BITS == 32

Posted by Peter Maydell 1 week ago
On Thu, 21 May 2020 at 14:58, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> Newer clangs rightly spot that you can never exceed the full address
> space of 64 bit hosts with:
>
>   linux-user/elfload.c:2076:41: error: result of comparison 'unsigned
>   long' > 18446744073709551615 is always false
>   [-Werror,-Wtautological-type-limit-compare]
>   4685         if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
>   4686             ~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
>   4687 1 error generated.
>
> So lets limit the check to 32 bit hosts only.

> +#if HOST_LONG_BITS == 32
>          if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
>              error_report("%s: requires more virtual address space "
>                           "than the host can provide (0x%" PRIx64 ")",
>                           image_name, (uint64_t)guest_hiaddr - guest_base);
>              exit(EXIT_FAILURE);
>          }
> +#endif

Is this also a tautological compare in the host==32 && guest==32
case? Do we maybe want "#if HOST_LONG_BITS < TARGET_ABI_BITS" ?

thanks
-- PMM