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Currently, "gcc-4.8.5-28.el7_5.1.x86_64" generates the following code for
me, from the XADD inline assembly added to "X64/GccInline.c" in commit
17634d026f96:
> 0000000000004383 <InternalSyncIncrement>:
> UINT32
> EFIAPI
> InternalSyncIncrement (
> IN volatile UINT32 *Value
> )
> {
> 4383: 55 push %rbp
> 4384: 48 89 e5 mov %rsp,%rbp
> 4387: 48 83 ec 10 sub $0x10,%rsp
> 438b: 48 89 4d 10 mov %rcx,0x10(%rbp)
> UINT32 Result;
>
> __asm__ __volatile__ (
> 438f: 48 8b 55 10 mov 0x10(%rbp),%rdx
> 4393: 48 8b 45 10 mov 0x10(%rbp),%rax
> 4397: b8 01 00 00 00 mov $0x1,%eax
> 439c: f0 0f c1 00 lock xadd %eax,(%rax)
> 43a0: ff c0 inc %eax
> 43a2: 89 45 fc mov %eax,-0x4(%rbp)
> : "m" (*Value) // %2
> : "memory",
> "cc"
> );
>
> return Result;
> 43a5: 8b 45 fc mov -0x4(%rbp),%eax
> }
> 43a8: c9 leaveq
> 43a9: c3 retq
>
The MOV $0X1,%EAX instruction corrupts the address of Value in %RAX before
we reach the XADD instruction. In fact, it makes no sense for XADD to use
%EAX as source operand and (%RAX) as destination operand at the same time.
The XADD instruction's destination operand is a read-write operand. The
GCC documentation states:
> The ordinary output operands must be write-only; GCC will assume that
> the values in these operands before the instruction are dead and need
> not be generated. Extended asm supports input-output or read-write
> operands. Use the constraint character `+' to indicate such an operand
> and list it with the output operands. You should only use read-write
> operands when the constraints for the operand (or the operand in which
> only some of the bits are to be changed) allow a register.
(The above is intentionally quoted from the oldest GCC release that edk2
supports, namely gcc-4.4:
<https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Extended-Asm.html>.)
Fix the operand list accordingly.
With the patch applied, I get:
> 0000000000004383 <InternalSyncIncrement>:
> UINT32
> EFIAPI
> InternalSyncIncrement (
> IN volatile UINT32 *Value
> )
> {
> 4383: 55 push %rbp
> 4384: 48 89 e5 mov %rsp,%rbp
> 4387: 48 83 ec 10 sub $0x10,%rsp
> 438b: 48 89 4d 10 mov %rcx,0x10(%rbp)
> UINT32 Result;
>
> __asm__ __volatile__ (
> 438f: 48 8b 55 10 mov 0x10(%rbp),%rdx
> 4393: 48 8b 45 10 mov 0x10(%rbp),%rax
> 4397: b8 01 00 00 00 mov $0x1,%eax
> 439c: f0 0f c1 02 lock xadd %eax,(%rdx)
> 43a0: ff c0 inc %eax
> 43a2: 89 45 fc mov %eax,-0x4(%rbp)
> : // no inputs that aren't also outputs
> : "memory",
> "cc"
> );
>
> return Result;
> 43a5: 8b 45 fc mov -0x4(%rbp),%eax
> }
> 43a8: c9 leaveq
> 43a9: c3 retq
Note that some other bugs remain in
"BaseSynchronizationLib/*/GccInline.c"; those should be addressed later,
under <https://bugzilla.tianocore.org/show_bug.cgi?id=1208>.
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1207
Fixes: 17634d026f968c404b039a8d8431b6389dd396ea
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
EDK II Project
A modern, feature-rich, cross-platform firmware development environment for the UEFI and PI specifications from www.uefi.org.
Contributions to the EDK II open source project are covered by the TianoCore Contribution Agreement 1.1
The majority of the content in the EDK II open source project uses a BSD 2-Clause License. The EDK II open source project contains the following components that are covered by additional licenses:
- AppPkg/Applications/Python/Python-2.7.2/Tools/pybench
- AppPkg/Applications/Python/Python-2.7.2
- AppPkg/Applications/Python/Python-2.7.10
- BaseTools/Source/C/BrotliCompress
- MdeModulePkg/Library/BrotliCustomDecompressLib
- OvmfPkg
- CryptoPkg/Library/OpensslLib/openssl
The EDK II Project is composed of packages. The maintainers for each package are listed in Maintainers.txt.