On 22/03/2021 12:10, Andrew Jones wrote:
So far we've counted on QEMU or kvmtool implicitly zeroing all memory.
With our goal of eventually supporting bare-metal targets with
target-efi we should explicitly zero any memory we expect to be zeroed
ourselves. This obviously includes the BSS, but also the bootcpu's
stack, as the bootcpu's thread-info lives in the stack and may get
used in early setup to get the cpu index. Note, this means we still
assume the bootcpu's cpu index to be zero. That assumption can be
removed later.
Cc: Nikos Nikoleris <nikos.nikoleris@xxxxxxx>
Cc: Alexandru Elisei <alexandru.elisei@xxxxxxx>
Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
Thanks for this Drew!
Good point about BSS too, I was worried about thread_info but in
target-efi BSS will be a problem too.
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@xxxxxxx>
---
arm/cstart.S | 22 ++++++++++++++++++++++
arm/cstart64.S | 23 ++++++++++++++++++++++-
arm/flat.lds | 6 ++++++
3 files changed, 50 insertions(+), 1 deletion(-)
diff --git a/arm/cstart.S b/arm/cstart.S
index ef936ae2f874..6de461ef94bf 100644
--- a/arm/cstart.S
+++ b/arm/cstart.S
@@ -15,12 +15,34 @@
#define THREAD_START_SP ((THREAD_SIZE - S_FRAME_SIZE * 8) & ~7)
+.macro zero_range, tmp1, tmp2, tmp3, tmp4
+ mov \tmp3, #0
+ mov \tmp4, #0
+9998: cmp \tmp1, \tmp2
+ beq 9997f
+ strd \tmp3, \tmp4, [\tmp1]
+ add \tmp1, \tmp1, #8
+ b 9998b
+9997:
+.endm
+
+
.arm
.section .init
.globl start
start:
+ /* zero BSS */
+ ldr r4, =bss
+ ldr r5, =ebss
+ zero_range r4, r5, r6, r7
+
+ /* zero stack */
+ ldr r4, =stackbase
+ ldr r5, =stacktop
+ zero_range r4, r5, r6, r7
+
/*
* set stack, making room at top of stack for cpu0's
* exception stacks. Must start wtih stackptr, not
diff --git a/arm/cstart64.S b/arm/cstart64.S
index 0428014aa58a..4dc5989ef50c 100644
--- a/arm/cstart64.S
+++ b/arm/cstart64.S
@@ -13,6 +13,15 @@
#include <asm/page.h>
#include <asm/pgtable-hwdef.h>
+.macro zero_range, tmp1, tmp2
+9998: cmp \tmp1, \tmp2
+ b.eq 9997f
+ stp xzr, xzr, [\tmp1]
+ add \tmp1, \tmp1, #16
+ b 9998b
+9997:
+.endm
+
.section .init
/*
@@ -51,7 +60,19 @@ start:
b 1b
1:
- /* set up stack */
+ /* zero BSS */
+ adrp x4, bss
+ add x4, x4, :lo12:bss
+ adrp x5, ebss
+ add x5, x5, :lo12:ebss
+ zero_range x4, x5
+
+ /* zero and set up stack */
+ adrp x4, stackbase
+ add x4, x4, :lo12:stackbase
+ adrp x5, stacktop
+ add x5, x5, :lo12:stacktop
+ zero_range x4, x5
mov x4, #1
msr spsel, x4
isb
diff --git a/arm/flat.lds b/arm/flat.lds
index 25f8d03cba87..8eab3472e2f2 100644
--- a/arm/flat.lds
+++ b/arm/flat.lds
@@ -17,7 +17,11 @@ SECTIONS
.rodata : { *(.rodata*) }
.data : { *(.data) }
+ . = ALIGN(16);
+ PROVIDE(bss = .);
.bss : { *(.bss) }
+ . = ALIGN(16);
+ PROVIDE(ebss = .);
. = ALIGN(64K);
PROVIDE(edata = .);
@@ -26,6 +30,8 @@ SECTIONS
* sp must be 16 byte aligned for arm64, and 8 byte aligned for arm
* sp must always be strictly less than the true stacktop
*/
+ . = ALIGN(16);
+ PROVIDE(stackbase = .);
. += 64K;
. = ALIGN(64K);
PROVIDE(stackptr = . - 16);
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