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[0/4] system: Forbid alloca()

Message ID 20250605193540.59874-1-philmd@linaro.org
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Series system: Forbid alloca() | expand

Message

Philippe Mathieu-Daudé June 5, 2025, 7:35 p.m. UTC 
Eradicate alloca() uses on system code, then enable
-Walloca to prevent new ones to creep back in.

Philippe Mathieu-Daudé (4):
  hw/gpio/pca9552: Avoid using g_newa()
  backends/tpmL Avoid using g_alloca()
  tests/unit/test-char: Avoid using g_alloca()
  buildsys: Prohibit alloca() use on system code

 meson.build                 | 4 ++++
 backends/tpm/tpm_emulator.c | 4 ++--
 hw/gpio/pca9552.c           | 2 +-
 tests/unit/test-char.c      | 3 +--
 4 files changed, 8 insertions(+), 5 deletions(-)

Comments

Pierrick Bouvier June 5, 2025, 8:53 p.m. UTC | #1 
On 6/5/25 12:35 PM, Philippe Mathieu-Daudé wrote:
> Eradicate alloca() uses on system code, then enable
> -Walloca to prevent new ones to creep back in.
> 
> Philippe Mathieu-Daudé (4):
>    hw/gpio/pca9552: Avoid using g_newa()
>    backends/tpmL Avoid using g_alloca()
>    tests/unit/test-char: Avoid using g_alloca()
>    buildsys: Prohibit alloca() use on system code
> 
>   meson.build                 | 4 ++++
>   backends/tpm/tpm_emulator.c | 4 ++--
>   hw/gpio/pca9552.c           | 2 +-
>   tests/unit/test-char.c      | 3 +--
>   4 files changed, 8 insertions(+), 5 deletions(-)
> 

Good idea!

For the series:
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Peter Maydell June 6, 2025, 8:37 a.m. UTC | #2 
On Thu, 5 Jun 2025 at 20:35, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>
> Eradicate alloca() uses on system code, then enable
> -Walloca to prevent new ones to creep back in.
>
> Philippe Mathieu-Daudé (4):
>   hw/gpio/pca9552: Avoid using g_newa()
>   backends/tpmL Avoid using g_alloca()
>   tests/unit/test-char: Avoid using g_alloca()
>   buildsys: Prohibit alloca() use on system code
>
>  meson.build                 | 4 ++++
>  backends/tpm/tpm_emulator.c | 4 ++--
>  hw/gpio/pca9552.c           | 2 +-
>  tests/unit/test-char.c      | 3 +--
>  4 files changed, 8 insertions(+), 5 deletions(-)

There is also a use of alloca() in target/ppc/kvm.c
in kvmppc_load_htab_chunk(), so I suspect that patch 4
here will break compilation on PPC hosts with KVM enabled.

thanks
-- PMM
Alex Bennée June 6, 2025, 8:44 a.m. UTC | #3 
Philippe Mathieu-Daudé <philmd@linaro.org> writes:

> Eradicate alloca() uses on system code, then enable
> -Walloca to prevent new ones to creep back in.

Should we also mention it in style.rst:

  Use of the ``malloc/free/realloc/calloc/valloc/memalign/posix_memalign``
  APIs is not allowed in the QEMU codebase. Instead of these routines,

>
> Philippe Mathieu-Daudé (4):
>   hw/gpio/pca9552: Avoid using g_newa()
>   backends/tpmL Avoid using g_alloca()
>   tests/unit/test-char: Avoid using g_alloca()
>   buildsys: Prohibit alloca() use on system code
>
>  meson.build                 | 4 ++++
>  backends/tpm/tpm_emulator.c | 4 ++--
>  hw/gpio/pca9552.c           | 2 +-
>  tests/unit/test-char.c      | 3 +--
>  4 files changed, 8 insertions(+), 5 deletions(-)
Philippe Mathieu-Daudé June 6, 2025, 8:53 a.m. UTC | #4 
On 6/6/25 10:37, Peter Maydell wrote:
> On Thu, 5 Jun 2025 at 20:35, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>>
>> Eradicate alloca() uses on system code, then enable
>> -Walloca to prevent new ones to creep back in.
>>
>> Philippe Mathieu-Daudé (4):
>>    hw/gpio/pca9552: Avoid using g_newa()
>>    backends/tpmL Avoid using g_alloca()
>>    tests/unit/test-char: Avoid using g_alloca()
>>    buildsys: Prohibit alloca() use on system code
>>
>>   meson.build                 | 4 ++++
>>   backends/tpm/tpm_emulator.c | 4 ++--
>>   hw/gpio/pca9552.c           | 2 +-
>>   tests/unit/test-char.c      | 3 +--
>>   4 files changed, 8 insertions(+), 5 deletions(-)
> 
> There is also a use of alloca() in target/ppc/kvm.c
> in kvmppc_load_htab_chunk(), so I suspect that patch 4
> here will break compilation on PPC hosts with KVM enabled.

Oops sorry I missed that one :/