other half of lazy relocation from glibc dl-trampoline

diff --git a/ldso/ldso/x86_64/resolve.S b/ldso/ldso/x86_64/resolve.S
new file mode 100644 (file)
index 0000000..5d55d0c
--- /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