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arm: userspace: Rework system call arguments

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This patch changes the ARM system calls to use registers for passing
or arguments.  This removes the possibility of stack issues when
callers do not adhere to the AAPCS.

Fixes #6802

Signed-off-by: Andy Gross <andy.gross@linaro.org>
This commit is contained in:
Andy Gross 2018-04-13 16:03:24 -05:00 • committed by Andrew Boie
commit 09a8810b33
3 changed files with 81 additions and 107 deletions
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21
arch/arm/core/swap_helper.S
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@ -368,25 +368,30 @@ _oops:
*
* On SVC exeption, the stack looks like the following:
* r0 - r1 - r2 - r3 - r12 - LR - PC - PSR
* r5 - r6 - call id - saved LR
*
* Registers look like:
* r0 - arg1
* r1 - arg2
* r2 - arg3
* r3 - arg4
* r4 - arg5
* r5 - arg6
* r6 - call_id
* r7 - saved link register
*/
_do_syscall:
ldr r1, [r0, #24] /* grab address of PC from stack frame */
str r1, [r0, #44] /* store address to use for LR after syscall */
ldr r7, [r0, #24] /* grab address of PC from stack frame */
ldr r1, =_arm_do_syscall
str r1, [r0, #24] /* overwrite the LR to point to _arm_do_syscall */
/* validate syscall limit, only set priv mode if valid */
ldr ip, =_SYSCALL_LIMIT
ldr r1, [r0, #40]
cmp r1, ip
cmp r6, ip
blt valid_syscall_id
/* bad syscall id. Set arg0 to bad id and set call_id to SYSCALL_BAD */
str r1, [r0, #0]
ldr r1, =_SYSCALL_BAD
str r1, [r0, #40]
str r6, [r0, #0]
ldr r6, =_SYSCALL_BAD
valid_syscall_id:
/* set mode to privileged, r2 still contains value from CONTROL */