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- /* -*- mode:c; c-basic-offset:4; tab-width:4; indent-tabs-mode:t; mode:auto-fill; fill-column:78; -*- */
- /* vim: set ts=4 sw=4 et tw=78 fo=cqt wm=0: */
- /* This is the canonical entry point, usually the first thing in the text
- segment. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry
- point runs, most registers' values are unspecified, except for:
- %rdx Contains a function pointer to be registered with `atexit'.
- This is how the dynamic linker arranges to have DT_FINI
- functions called for shared libraries that have been loaded
- before this code runs.
- %rsp The stack contains the arguments and environment:
- 0(%rsp) argc
- 8(%rsp) argv[0]
- ...
- (8*argc)(%rsp) NULL
- (8*(argc+1))(%rsp) envp[0]
- ...
- NULL
- */
- .text
- .globl shim_start
- .type shim_start,@function
- shim_start:
- .cfi_startproc
- /* Clear the frame pointer. The ABI suggests this be done, to mark
- the outermost frame obviously. */
- xorq %rbp, %rbp
- movq %rsp, %rbp
- /* Extract the arguments as encoded on the stack and set up
- the arguments for shim_init (int, void *, void **),
- The arguments are passed via registers and on the stack:
- argc: %rdi
- argv: %rsi
- */
- /* Align the stack to a 16 byte boundary to follow the ABI. */
- andq $~15, %rsp
- movq %rdi, %rcx /* Possibly the stack has to be switched */
- movq 0(%rbp), %rdi /* Pop the argument count. */
- leaq 8(%rbp), %rsi /* argv starts just at the current stack top. */
- pushq %rdx
- movq shim_init@GOTPCREL(%rip), %r11
- call *%r11
- retq
- .cfi_endproc
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