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[ld.so] Properly handle stack alignment in ld.so args

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Now when loading a process, init will push all the loader args, align
the stack so that the next pointer will have correct alignment, then
push a pointer to the loader args.

Also:
* _ldso_start will pop all loader args off of the stack before jumping
  to the loaded program's entrypoint, as if it had never run.
* The sentinel arg structures have a size instead of being all zeros, so
  that they can be popped off properly when done.
This commit is contained in:
Justin C. Miller
2024-02-20 19:42:12 -08:00
parent e17119254b
commit 9f8e75f680
3 changed files with 28 additions and 5 deletions
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12
src/user/srv.init/loader.cpp
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@@ -49,7 +49,7 @@ stack_push_sentinel(uint8_t *&stack)
memset(stack, 0, size);
j6_arg_header *header = reinterpret_cast<j6_arg_header*>(stack);
header->type = j6_arg_type_none;
header->size = 0;
header->size = size;
}
template <typename T> T *
@@ -222,6 +222,7 @@ load_program(
uintptr_t entrypoint = program_elf.entrypoint() + program_image_base;
if (dyn) {
stack_push_sentinel(stack);
j6_arg_loader *loader_arg = stack_push<j6_arg_loader>(stack, 0);
const elf::file_header *h = program_elf.header();
loader_arg->image_base = program_image_base;
@@ -240,6 +241,15 @@ load_program(
handles_arg->handles[1].handle = vfs;
handles_arg->handles[1].proto = j6::proto::vfs::id;
// Align the stack to be one word short of 16-byte aligned, so
// that the arg address will be aligned when pushed
while ((reinterpret_cast<uintptr_t>(stack) & 0xf) != 0x8) --stack;
// Push the args list address itself
stack -= sizeof(uintptr_t);
uintptr_t *args_addr = reinterpret_cast<uintptr_t*>(stack);
*args_addr = stack_top - (stack_orig - reinterpret_cast<uint8_t*>(handles_arg));
uintptr_t ldso_image_base = (eop & ~(MiB-1)) + MiB;
for (auto seg : program_elf.segments()) {