diff mbox series

[v2,4/5] crypto: x86/crc32c - Use idiomatic relative jump table

Message ID 20241010122801.1321976-11-ardb+git@google.com (mailing list archive)
State Superseded
Headers show
Series Improve objtool jump table handling | expand

Commit Message

Ard Biesheuvel Oct. 10, 2024, 12:28 p.m. UTC 
From: Ard Biesheuvel <ardb@kernel.org>

The original crc32c code used a place-relative jump table but with a
slightly awkward use of two separate symbols. To help objtool, this was
replaced with a bog-standard position dependent jump table call, which
was subsequently tweaked to use a RIP-relative reference to the table,
but still populate it with absolute 64-bit references.

Given that objtool will need to be taught about the jump table idiom
that compilers use when running with -fpie enabled, let's update the
jump table in the crc32c code once again to use this standard idiom,
where the jump table carries 32-bit references relative to the start of
the table, and the destination address can be obtained by adding the
two.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/crypto/crc32c-pcl-intel-asm_64.S | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
index bbcff1fb78cb..45b005935194 100644
--- a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
+++ b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
@@ -53,7 +53,7 @@ 
 .endm
 
 .macro JMPTBL_ENTRY i
-.quad .Lcrc_\i
+.long .Lcrc_\i - jump_table
 .endm
 
 .macro JNC_LESS_THAN j
@@ -169,7 +169,8 @@  SYM_FUNC_START(crc_pcl)
 
 	## branch into array
 	leaq	jump_table(%rip), %bufp
-	mov	(%bufp,%rax,8), %bufp
+	movslq	(%bufp,%rax,4), len
+	addq	len, %bufp
 	JMP_NOSPEC bufp
 
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