Commit 2a803c4d authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
Browse files

arm64: head.S: use memset to clear BSS

Currently we use an open-coded memzero to clear the BSS. As it is a
trivial implementation, it is sub-optimal.

Our optimised memset doesn't use the stack, is position-independent, and
for the memzero case can use of DC ZVA to clear large blocks
efficiently. In __mmap_switched the MMU is on and there are no live
caller-saved registers, so we can safely call an uninstrumented memset.

This patch changes __mmap_switched to use memset when clearing the BSS.
We use the __pi_memset alias so as to avoid any instrumentation in all
kernel configurations.

Cc: Catalin Marinas <>
Cc: Marc Zyngier <>
Reviewed-by: default avatarArd Biesheuvel <>
Signed-off-by: default avatarMark Rutland <>
Signed-off-by: default avatarWill Deacon <>
parent b523e185
......@@ -415,14 +415,13 @@ ENDPROC(__create_page_tables)
.set initial_sp, init_thread_union + THREAD_START_SP
adr_l x6, __bss_start
adr_l x7, __bss_stop
1: cmp x6, x7
b.hs 2f
str xzr, [x6], #8 // Clear BSS
b 1b
// Clear BSS
adr_l x0, __bss_start
mov x1, xzr
adr_l x2, __bss_stop
sub x2, x2, x0
bl __pi_memset
adr_l sp, initial_sp, x4
mov x4, sp
and x4, x4, #~(THREAD_SIZE - 1)
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