diff options
| -rw-r--r-- | ldso/ldso/x86_64/resolve.S | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/ldso/ldso/x86_64/resolve.S b/ldso/ldso/x86_64/resolve.S new file mode 100644 index 000000000..5d55d0c73 --- /dev/null +++ b/ldso/ldso/x86_64/resolve.S @@ -0,0 +1,63 @@ +/* + * This function is _not_ called directly. It is jumped to (so no return + * address is on the stack) when attempting to use a symbol that has not yet + * been resolved. The first time a jump symbol (such as a function call inside + * a shared library) is used (before it gets resolved) it will jump here to + * _dl_linux_resolve. When we get called the stack looks like this: + * reloc_entry + * tpnt + * + * This function saves all the registers, puts a copy of reloc_entry and tpnt + * on the stack (as function arguments) then make the function call + * _dl_linux_resolver(tpnt, reloc_entry). _dl_linux_resolver() figures out + * where the jump symbol is _really_ supposed to have jumped to and returns + * that to us. Once we have that, we overwrite tpnt with this fixed up + * address. We then clean up after ourselves, put all the registers back how we + * found them, then we jump to where the fixed up address, which is where the + * jump symbol that got us here really wanted to jump to in the first place. + * found them, then we jump to the fixed up address, which is where the jump + * symbol that got us here really wanted to jump to in the first place. + * -Erik Andersen + */ + +/* more info taken from glibc/sysdeps/x86_64/dl-trampoline.S */ + +.text + +.global _dl_linux_resolve +.type _dl_linux_resolve,%function +.align 16 + +_dl_linux_resolve: + subq $56,%rsp + /* Preserve registers otherwise clobbered. */ + movq %rax, (%rsp) + movq %rcx, 8(%rsp) + movq %rdx, 16(%rsp) + movq %rsi, 24(%rsp) + movq %rdi, 32(%rsp) + movq %r8, 40(%rsp) + movq %r9, 48(%rsp) + + movq 64(%rsp), %rsi /* Copy args pushed by PLT in register. */ + movq %rsi, %r11 /* Multiply by 24 */ + addq %r11, %rsi + addq %r11, %rsi + shlq $3, %rsi + movq 56(%rsp), %rdi /* %rdi: link_map, %rsi: reloc_offset */ + call _dl_linux_resolver /* Call resolver. */ + movq %rax, %r11 /* Save return value */ + + /* Get register content back. */ + movq 48(%rsp), %r9 + movq 40(%rsp), %r8 + movq 32(%rsp), %rdi + movq 24(%rsp), %rsi + movq 16(%rsp), %rdx + movq 8(%rsp), %rcx + movq (%rsp), %rax + + addq $72, %rsp /* Adjust stack(PLT did 2 pushes) */ + jmp *%r11 /* Jump to function address. */ + +.size _dl_linux_resolve,.-_dl_linux_resolve |