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armv7-m: Fix syscall stack alignment

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This fixes "df -h" with PROTECTED build.  Tested on qemu.

Reference:
	aapcs32 "6.2.1 The Stack/Stack constraints at a public interface"
This commit is contained in:
YAMAMOTO Takashi 2020-02-26 02:25:55 +09:00 committed by patacongo
parent 1f1356a2f5
commit 9a8169acdf
1 changed files with 14 additions and 2 deletions
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16
arch/arm/src/armv7-m/up_svcall.c
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@ -97,16 +97,28 @@ static void dispatch_syscall(void)
{
__asm__ __volatile__
(
" sub sp, sp, #16\n" /* Create a stack frame to hold 3 parms + lr */
/* Create a stack frame to hold 3 parameters + LR and SP adjustment value.
* Also, Ensure 8 bytes alignment. We use IP as a scratch.
*
* NOTE: new_SP = (orig_SP - 20) & ~7
* = orig_SP - 20 - ((orig_SP - 20) & ~7)
*/
" mov ip, sp\n" /* Calculate (orig_SP - new_SP) */
" sub ip, ip, #20\n"
" and ip, ip, #7\n"
" add ip, ip, #20\n"
" sub sp, sp, ip\n"
" str r4, [sp, #0]\n" /* Move parameter 4 (if any) into position */
" str r5, [sp, #4]\n" /* Move parameter 5 (if any) into position */
" str r6, [sp, #8]\n" /* Move parameter 6 (if any) into position */
" str lr, [sp, #12]\n" /* Save lr in the stack frame */
" str ip, [sp, #16]\n" /* Save (orig_SP - new_SP) value */
" ldr ip, =g_stublookup\n" /* R12=The base of the stub lookup table */
" ldr ip, [ip, r0, lsl #2]\n" /* R12=The address of the stub for this syscall */
" blx ip\n" /* Call the stub (modifies lr) */
" ldr lr, [sp, #12]\n" /* Restore lr */
" add sp, sp, #16\n" /* Destroy the stack frame */
" ldr r2, [sp, #16]\n" /* Restore (orig_SP - new_SP) value */
" add sp, sp, r2\n" /* Restore SP */
" mov r2, r0\n" /* R2=Save return value in R2 */
" mov r0, #3\n" /* R0=SYS_syscall_return */
" svc 0" /* Return from the syscall */