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authorMark Rutland <mark.rutland@arm.com>2021-10-19 17:02:07 +0100
committerWill Deacon <will@kernel.org>2021-10-21 10:45:21 +0100
commit35d67794b88283337e0d311a4dbacc42d07a12a5 (patch)
tree5a5838757278b50059301388a669efe027c5ffb7 /arch/arm64/lib
parent5816b3e6577eaa676ceb00a848f0fd65fe2adc29 (diff)
arm64: lib: __arch_clear_user(): fold fixups into body
Like other functions, __arch_clear_user() places its exception fixups in the `.fixup` section without any clear association with __arch_clear_user() itself. If we backtrace the fixup code, it will be symbolized as an offset from the nearest prior symbol, which happens to be `__entry_tramp_text_end`. Further, since the PC adjustment for the fixup is akin to a direct branch rather than a function call, __arch_clear_user() itself will be missing from the backtrace. This is confusing and hinders debugging. In general this pattern will also be problematic for CONFIG_LIVEPATCH, since fixups often return to their associated function, but this isn't accurately captured in the stacktrace. To solve these issues for assembly functions, we must move fixups into the body of the functions themselves, after the usual fast-path returns. This patch does so for __arch_clear_user(). Inline assembly will be dealt with in subsequent patches. Other than the improved backtracing, there should be no functional change as a result of this patch. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Robin Murphy <robin.murphy@arm.com> Reviewed-by: Ard Biesheuvel <ardb@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Mark Brown <broonie@kernel.org> Cc: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20211019160219.5202-2-mark.rutland@arm.com Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/lib')
-rw-r--r--arch/arm64/lib/clear_user.S8
1 files changed, 3 insertions, 5 deletions
diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index a7efb2ad2a1c..2827fddc33f8 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S
@@ -45,13 +45,11 @@ USER(9f, sttrh wzr, [x0])
USER(7f, sttrb wzr, [x2, #-1])
5: mov x0, #0
ret
-SYM_FUNC_END(__arch_clear_user)
-EXPORT_SYMBOL(__arch_clear_user)
- .section .fixup,"ax"
- .align 2
+ // Exception fixups
7: sub x0, x2, #5 // Adjust for faulting on the final byte...
8: add x0, x0, #4 // ...or the second word of the 4-7 byte case
9: sub x0, x2, x0
ret
- .previous
+SYM_FUNC_END(__arch_clear_user)
+EXPORT_SYMBOL(__arch_clear_user)