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| -rw-r--r-- | docs/exec-formats-and-tools.md | 56 |
1 files changed, 50 insertions, 6 deletions
diff --git a/docs/exec-formats-and-tools.md b/docs/exec-formats-and-tools.md index 9aefeb7..3d9e7e8 100644 --- a/docs/exec-formats-and-tools.md +++ b/docs/exec-formats-and-tools.md @@ -100,7 +100,7 @@ Compile Executables with 'mips-linux-gnu' Toolchain The Linux targetting toolchains use a MIPS O32 ABI calling convention which allows building position-independent -binaries and overcome missing PC relative support +binaries (PIC, PIE) and overcome missing PC relative support in the basic MIPS instruction set. The ABI uses strictly convention equivalent to calling each function indirectly through 't9' register ('jalr t9'). The known value pointing @@ -127,17 +127,17 @@ next: .set noreorder .cpload $31 .set reorder - addi a0, zero, 0 - addi a1, zero, 0 + addi $a0, $zero, 0 + addi $a1, $zero, 0 jal main quit: - addi a0, zero, 0 - addi v0, zero, 4001 /* SYS_exit */ + addi $a0, $zero, 0 + addi $v0, $zero, 4001 /* SYS_exit */ syscall loop: break - beq zero, zero, loop + beq $zero, $zero, loop nop .end __start @@ -240,3 +240,47 @@ and allows code compiled agains musl C library to start as well. mips-linux-gnu-gcc -ggdb -O1 -march=mips2 -static -specs=/opt/musl/mips-linux-gnu/lib/musl-gcc.specs -c program.c -o program.o mips-linux-gnu-gcc -ggdb -march=mips2 -static -specs=/opt/musl/mips-linux-gnu/lib/musl-gcc.specs programo -o program ``` + +The C library startup code which support both PIC/PIE and non-PIC environment + +``` +/* minimal replacement of crt0.o which is else provided by C library */ +/* this variant support both static and PIC/PIE environments */ + +.globl main +.globl _start +.globl __start +.set noat +.set noreorder +.ent _start + +.text + +__start: +_start: +#if defined(__PIC__) || defined(__pic__) + bal next + nop +next: + .set noreorder + .cpload $31 + .set reorder +#else + la $gp, _gp +#endif + addi $a0, $zero, 0 + addi $a1, $zero, 0 + jal main + nop +quit: + addi $a0, $zero, 0 + addi $v0, $zero, 4001 /* SYS_exit */ + + syscall + +loop: break + beq $zero, $zero, loop + nop + +.end _start +``` |