[PATCH] tools/nolibc: sh: enter _start_c with jsr instead of bsr

[PATCH] tools/nolibc: sh: enter _start_c with jsr instead of bsr

[Daniel Palmer]

bsr has limited displacement and cannot reach _start_c if its
more than +/-4KiB away.

This starts to show up if you have big programs (static binary
of the game Quake in my case) and/or use LTO and things get moved
around.

Replace bsr with a calculation of the effective address of
_start_c and jsr.

Tested on QEMU and real SH4 and SH4a machines.

Signed-off-by: Daniel Palmer <daniel@0x0f.com>
---

I'm no SuperH asm expert but this works for me. :)
Maybe there is a way in C to get _start and _start_c to always
be close together that would avoid this entirely?

 tools/include/nolibc/arch-sh.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/include/nolibc/arch-sh.h b/tools/include/nolibc/arch-sh.h
index 996cfbe1bee3..7318f52dcba9 100644
--- a/tools/include/nolibc/arch-sh.h
+++ b/tools/include/nolibc/arch-sh.h
@@ -154,8 +154,13 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __nolibc_no_stack_prote
 		"_start:\n"
 
 		"mov sp, r4\n"               /* save argc pointer to r4, as arg1 of _start_c */
-		"bsr _start_c\n"             /* transfer to c runtime                        */
+		"mova 1f, r0\n"              /* load the effective address of 1: into r0     */
+		"mov.l @r0, r1\n"            /* load the distance to _start_c from 1:        */
+		"add r0, r1\n"               /* calculate address of _start_c                */
+		"jsr @r1\n"                  /* transfer to c runtime                        */
 		"nop\n"                      /* delay slot                                   */
+		".balign 4\n"
+		"1: .long _start_c - 1b\n"   /* Distance from here to _start_c               */
 
 		".size _start, .-_start\n"
 	);
-- 
2.55.0