svn commit: r326752 - head/stand/arm/uboot
Ian Lepore
ian at FreeBSD.org
Sun Dec 10 21:51:28 UTC 2017
Author: ian
Date: Sun Dec 10 21:51:27 2017
New Revision: 326752
URL: https://svnweb.freebsd.org/changeset/base/326752
Log:
Save and restore r9 register in arm ubldr. In old gcc 4.2, r9 was a callee-
saved register, but in arm EABI it may be either callee-saved or dedicated
to some special purpose (such as a TLS pointer). It appears clang does not
treat it as a callee-saved register (instead using it as another work
register, similar to r12).
Another important side effect of these changes is that saving an extra
register in the push/pop statements keeps the stack aligned to an 8-byte
boundary during the self_reloc() call, as it always should have been.
As stated in the PR...
Essentially the important caller-saved registers are pushed (r0, r1, r9, lr)
before the relocation call, and popped after. Then r8/r9 are saved as usual
for the syscall trampoline, and lr is stored in r8 (now free) as a
callee-saved value before calling into `main`.
The call to `main` can no longer be a tail call because we must restore r9
especially after main returns (although since we have used r8 to hold lr we
must also restore this).
PR: 224008
Modified:
head/stand/arm/uboot/start.S
Modified: head/stand/arm/uboot/start.S
==============================================================================
--- head/stand/arm/uboot/start.S Sun Dec 10 19:22:43 2017 (r326751)
+++ head/stand/arm/uboot/start.S Sun Dec 10 21:51:27 2017 (r326752)
@@ -46,11 +46,8 @@ _start:
mcr p15, 0, ip, c1, c0, 0
#endif
- /*
- * Save r0 and r1 (argc and argv passed from u-boot), and lr (trashed
- * by the call to self_reloc below) until we're ready to call main().
- */
- push {r0, r1, lr}
+ /* Save the arguments and return register before calling self_reloc */
+ push {r0, r1, r9, lr}
/*
* Do self-relocation when the weak external symbol _DYNAMIC is non-NULL.
@@ -68,22 +65,31 @@ _start:
addne r1, r1, r0 /* r1 = dynamic section physaddr. */
blne _C_LABEL(self_reloc) /* Do reloc if _DYNAMIC is non-NULL. */
+ /* Restore saved arguments */
+ pop {r0, r1, r9, lr}
+
/* Hint where to look for the API signature */
ldr ip, =uboot_address
str sp, [ip]
- /* Save U-Boot's r8 and r9 */
+ /* Save U-Boot's r8 and r9 for syscall trampoline */
ldr ip, =saved_regs
- str r8, [ip, #0]
- str r9, [ip, #4]
+ str r8, [ip, #0] /* old gd pointer (use to hold lr) */
+ str r9, [ip, #4] /* new gd pointer */
/*
- * First restore argc, argv, and the u-boot return address, then
- * Start loader. This is basically a tail-recursion call; if main()
- * returns, it returns to u-boot (which reports the value returned r0).
+ * Start loader. Save return address first (r8 is available from
+ * trampoline save).
*/
- pop {r0, r1, lr}
- b main
+ mov r8, lr
+ bl main
+ mov lr, r8
+
+ /* Restore U-Boot environment */
+ ldr ip, =saved_regs
+ ldr r8, [ip, #0]
+ ldr r9, [ip, #4]
+ mov pc, lr
/*
* Data for self-relocation, in the text segment for pc-rel access.
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