path: root/Documentation
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authorNicholas Piggin <npiggin@gmail.com>2021-05-20 21:19:30 +1000
committerMichael Ellerman <mpe@ellerman.id.au>2021-05-21 00:58:03 +1000
commit5665bc35c1ed917ac8fd06cb651317bb47a65b10 (patch)
treea2be9f6c1edc3cbda85fcdd9d171591a6fb593d6 /Documentation
parente2f5efd0f0e229bd110eab513e7c0331d61a4649 (diff)
powerpc/64s/syscall: Use pt_regs.trap to distinguish syscall ABI difference between sc and scv syscalls
The sc and scv 0 system calls have different ABI conventions, and ptracers need to know which system call type is being used if they want to look at the syscall registers. Document that pt_regs.trap can be used for this, and fix one in-tree user to work with scv 0 syscalls. Fixes: 7fa95f9adaee ("powerpc/64s: system call support for scv/rfscv instructions") Cc: stable@vger.kernel.org # v5.9+ Reported-by: "Dmitry V. Levin" <ldv@altlinux.org> Suggested-by: "Dmitry V. Levin" <ldv@altlinux.org> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20210520111931.2597127-1-npiggin@gmail.com
Diffstat (limited to 'Documentation')
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/powerpc/syscall64-abi.rst b/Documentation/powerpc/syscall64-abi.rst
index dabee3729e5a..56490c4c0c07 100644
--- a/Documentation/powerpc/syscall64-abi.rst
+++ b/Documentation/powerpc/syscall64-abi.rst
@@ -109,6 +109,16 @@ auxiliary vector.
scv 0 syscalls will always behave as PPC_FEATURE2_HTM_NOSC.
+When ptracing system calls (PTRACE_SYSCALL), the pt_regs.trap value contains
+the system call type that can be used to distinguish between sc and scv 0
+system calls, and the different register conventions can be accounted for.
+If the value of (pt_regs.trap & 0xfff0) is 0xc00 then the system call was
+performed with the sc instruction, if it is 0x3000 then the system call was
+performed with the scv 0 instruction.

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