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From: Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>
To: Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH v3 13/13] aarch64: fix _mcount for pac-ret
Date: Tue, 26 May 2020 16:13:26 -0300	[thread overview]
Message-ID: <aa215c72-3b07-8f0c-c1e0-428108775fc8@linaro.org> (raw)
In-Reply-To: <20200526183853.GA24512@arm.com>



On 26/05/2020 15:38, Szabolcs Nagy wrote:
> The 05/26/2020 08:33, Adhemerval Zanella via Libc-alpha wrote:
>>
>>
>> On 15/05/2020 11:40, Szabolcs Nagy wrote:
>>> gcc -pg with -mbranch-protection=pac-ret passes signed return address
>>> to _mcount, so _mcount now has to always strip pac from the frompc
>>> since that's from user code that may be built with pac-ret.
>>>
>>> This is a backward incompatible _mcount abi change introduced by
>>> return address signing support in gcc-7.
>>
>> Which change are you referring about specifically?
> 
> gcc-7 introduced -msigned-return-address (which was
> later deprecated by -mbranch-protection=pac-ret) and
> the code generation with -pg is not compatible with
> existing _mcount runtime implementations (because
> now _mcount needs unconditional xpac)

Thanks, could you add this explanation on commit message as
well?

> 
> i'm still trying to see if this _mcount change is
> needed or we can change gcc to do the right thing
> (and not pass signed address to _mcount), but i
> need internal consensus about such abi break first.
> 
>>
>> Besides it, LGTM.
>>
>> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
>>
>>>
>>> TODO: fix -pg on the gcc side?
>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94791
>>> ---
>>>  sysdeps/aarch64/machine-gmon.h | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/sysdeps/aarch64/machine-gmon.h b/sysdeps/aarch64/machine-gmon.h
>>> index 730a23b781..328cbdda16 100644
>>> --- a/sysdeps/aarch64/machine-gmon.h
>>> +++ b/sysdeps/aarch64/machine-gmon.h
>>> @@ -30,5 +30,5 @@ static inline void mcount_internal (u_long frompc, u_long selfpc)
>>>  #define MCOUNT                                                    \
>>>  void __mcount (void *frompc)                                      \
>>>  {                                                                 \
>>> -  mcount_internal ((u_long) frompc, (u_long) RETURN_ADDRESS (0)); \
>>> +  mcount_internal ((u_long) strip_pac (frompc), (u_long) RETURN_ADDRESS (0)); \
>>>  }
>>>
> 

      reply	other threads:[~2020-05-26 19:13 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-15 14:40 [PATCH v3 00/13] aarch64: branch protection support Szabolcs Nagy
2020-05-15 14:40 ` [PATCH v3 01/13] elf.h: Add PT_GNU_PROPERTY Szabolcs Nagy
2020-05-15 14:40 ` [PATCH v3 02/13] elf.h: add aarch64 property definitions Szabolcs Nagy
2020-05-18 15:26   ` Florian Weimer via Libc-alpha
2020-05-21  8:57     ` Szabolcs Nagy
2020-05-15 14:40 ` [PATCH v3 03/13] Rewrite abi-note.S in C Szabolcs Nagy
2020-05-18 15:28   ` Florian Weimer via Libc-alpha
2020-05-20 10:27     ` Szabolcs Nagy
2020-05-20 10:34       ` Florian Weimer via Libc-alpha
2020-05-21  8:54         ` [PATCH v4] " Szabolcs Nagy
2020-05-15 14:40 ` [PATCH v3 04/13] aarch64: configure test for BTI support Szabolcs Nagy
2020-05-25 18:41   ` Adhemerval Zanella via Libc-alpha
2020-05-25 18:48     ` Adhemerval Zanella via Libc-alpha
2020-05-15 14:40 ` [PATCH v3 05/13] aarch64: Add BTI support to assembly files Szabolcs Nagy
2020-05-25 18:49   ` Adhemerval Zanella via Libc-alpha
2020-05-15 14:40 ` [PATCH v3 06/13] aarch64: Rename place holder .S files to .c Szabolcs Nagy
2020-05-15 14:40 ` [PATCH v3 07/13] aarch64: fix swapcontext for BTI Szabolcs Nagy
2020-05-15 14:40 ` [PATCH v3 08/13] aarch64: fix RTLD_START " Szabolcs Nagy
2020-05-15 14:40 ` [PATCH v3 09/13] aarch64: enable BTI at runtime Szabolcs Nagy
2020-05-25 19:53   ` Adhemerval Zanella via Libc-alpha
2020-05-26 11:20     ` Szabolcs Nagy
2020-05-15 14:40 ` [PATCH v3 10/13] aarch64: configure check for pac-ret code generation Szabolcs Nagy
2020-05-25 21:49   ` Adhemerval Zanella via Libc-alpha
2020-05-15 14:40 ` [PATCH v3 11/13] aarch64: Add pac-ret support to assembly files Szabolcs Nagy
2020-05-26 11:26   ` Adhemerval Zanella via Libc-alpha
2020-05-15 14:40 ` [PATCH v3 12/13] aarch64: redefine RETURN_ADDRESS to strip PAC Szabolcs Nagy
2020-05-26 11:29   ` Adhemerval Zanella via Libc-alpha
2020-05-15 14:40 ` [PATCH v3 13/13] aarch64: fix _mcount for pac-ret Szabolcs Nagy
2020-05-26 11:33   ` Adhemerval Zanella via Libc-alpha
2020-05-26 18:38     ` Szabolcs Nagy
2020-05-26 19:13       ` Adhemerval Zanella via Libc-alpha [this message]

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