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-rw-r--r--ldso/ldso/x86_64/resolve.S63
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