[coreboot-gerrit] New patch to review for coreboot: libpayload: head.S: Avoid clearing BSS (and heap) again

[Julius Werner (jwerner@chromium.org)]

Julius Werner (jwerner at chromium.org) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/16091

-gerrit

commit b5a7d1c83fbeee1ff4215c7d801849f34beff14b
Author: Julius Werner <jwerner at chromium.org>
Date:   Fri Aug 5 21:27:47 2016 -0700

    libpayload: head.S: Avoid clearing BSS (and heap) again
    
    3 out of 4 architectures currently zero out the payload BSS in early
    assembly code, which is pointless since the code loading the payload has
    already done that (with a more efficient memset). ARM64 has never had
    any code like this and can run just fine without it. This also defeats
    the new optimization of moving the heap out of the BSS, since all three
    implementations assume that everything between _edata and _end is BSS.
    We should just take this out.
    
    Change-Id: I45cd2dabd94da43ff0f77e990f11c877cee6cda1
    Signed-off-by: Julius Werner <jwerner at chromium.org>
---
 payloads/libpayload/arch/arm/head.S  | 19 -------------------
 payloads/libpayload/arch/mips/head.S | 10 ----------
 payloads/libpayload/arch/x86/head.S  |  8 --------
 3 files changed, 37 deletions(-)

diff --git a/payloads/libpayload/arch/arm/head.S b/payloads/libpayload/arch/arm/head.S
index 788e328..299faf2 100644
--- a/payloads/libpayload/arch/arm/head.S
+++ b/payloads/libpayload/arch/arm/head.S
@@ -33,22 +33,6 @@
  * Our entry point
  */
 ENTRY(_entry)
-
-	/* TODO: disable interrupts */
-
-	/* Clear BSS */
-	mov r12, #0
-	ldr r2, bss_boundaries
-	ldr r3, bss_boundaries + 4
-	cmp r2, r3
-	beq no_bss
-
-	sub r3, #4 /* Account for late condition check. */
-loop:
-	cmp r2, r3
-	str r12, [r2], #4
-	blt loop
-no_bss:
 	/* Save off the location of the coreboot tables */
 	ldr r1, 1f
 	str r0, [r1]
@@ -70,9 +54,6 @@ no_bss:
 ENDPROC(_entry)
 
 .align 4
-bss_boundaries:
-	.word _edata
-	.word _end
 1:
 .word	cb_header_ptr
 2:
diff --git a/payloads/libpayload/arch/mips/head.S b/payloads/libpayload/arch/mips/head.S
index c143e95..203e0ae 100644
--- a/payloads/libpayload/arch/mips/head.S
+++ b/payloads/libpayload/arch/mips/head.S
@@ -74,16 +74,6 @@ _entry:
 1:
 	lw	$gp, 0($ra)
 
-	/* Clear .bss: start_bss = _edata, end_bss = _end */
-	la	$t0, _edata
-	sw	$zero, ($t0)
-	la	$t1, _end - 4
-clear_bss:
-	addiu	$t0, 4
-	sw	$zero, ($t0)
-	bne	$t0, $t1, clear_bss
-	nop
-
 	/* Save off the location of the coreboot tables */
 	la	$at, cb_header_ptr
 	sw	$a0, 0x00($at)
diff --git a/payloads/libpayload/arch/x86/head.S b/payloads/libpayload/arch/x86/head.S
index 3dd6133..fa9bb73 100644
--- a/payloads/libpayload/arch/x86/head.S
+++ b/payloads/libpayload/arch/x86/head.S
@@ -73,14 +73,6 @@ _init:
 	movl %eax,loader_eax
 	movl %ebx,loader_ebx
 
-	/* Clear the bss */
-	cld
-	movl $.bss, %edi
-	movl $_end, %ecx
-	subl %edi, %ecx
-	xor %ax, %ax
-	rep stosb
-
 	/* Setup new stack. */
 	movl $_stack, %ebx