Loading `libvulkan.so.1` on Linux with `std.ElfDynLib` Part 2
2025-02-13This was originally a topic on Ziggit.
Spent some time on this today; and I got it to the point where it’s recursively loading libraries and applying relocations. I hope I’m doing the relocations correctly, I haven’t made a test program to check. Maybe I should do that.
Currently stuck at handling relocations that have to do with thread local storage:
debug: needed library: 0x1c73 libc.so.6
debug: needed library: 0x869c ld-linux-x86-64.so.2
debug: ld-linux-x86-64.so.2 loaded at 0x712c95391000 - 0x712c953c9310
warning: unhandled relocation(libc.so.6)[0001]: 0x001e7c68 <- "" (0x0) elf.R_X86_64.TPOFF64 56
warning: unhandled relocation(libc.so.6)[0002]: 0x001e7c70 <- "" (0x0) elf.R_X86_64.TPOFF64 48
warning: unhandled relocation(libc.so.6)[0003]: 0x001e7c78 <- "" (0x0) elf.R_X86_64.TPOFF64 72
warning: unhandled relocation(libc.so.6)[0004]: 0x001e7c80 <- "" (0x0) elf.R_X86_64.TPOFF64 88
warning: unhandled relocation(libc.so.6)[0005]: 0x001e7c88 <- "" (0x0) elf.R_X86_64.TPOFF64 80
warning: unhandled relocation(libc.so.6)[0006]: 0x001e7c90 <- "" (0x0) elf.R_X86_64.TPOFF64 100
warning: unhandled relocation(libc.so.6)[0007]: 0x001e7c98 <- "" (0x0) elf.R_X86_64.TPOFF64 120
warning: unhandled relocation(libc.so.6)[0008]: 0x001e7ca0 <- "" (0x0) elf.R_X86_64.TPOFF64 128
warning: unhandled relocation(libc.so.6)[0009]: 0x001e7cc0 <- "" (0x0) elf.R_X86_64.TPOFF64 24
warning: unhandled relocation(libc.so.6)[0010]: 0x001e7cd8 <- "" (0x0) elf.R_X86_64.TPOFF64 40
warning: unhandled relocation(libc.so.6)[0011]: 0x001e7cf0 <- "" (0x0) elf.R_X86_64.TPOFF64 16
warning: unhandled relocation(libc.so.6)[0012]: 0x001e7d78 <- "" (0x0) elf.R_X86_64.TPOFF64 96
warning: unhandled relocation(libc.so.6)[0013]: 0x001e7ef8 <- "" (0x0) elf.R_X86_64.TPOFF64 0
warning: unhandled relocation(libc.so.6)[0014]: 0x001e7fd8 <- "" (0x0) elf.R_X86_64.TPOFF64 8
warning: unhandled relocation(libc.so.6)[0015]: 0x001e7ff0 <- "" (0x0) elf.R_X86_64.TPOFF64 32
warning: unhandled relocation(libc.so.6)[0074]: 0x001e7ed0 <- "__libc_dlerror_result" (0x5f7) elf.R_X86_64.TPOFF64 0
debug: libc.so.6 loaded at 0x712c95402000 - 0x712c955f3c78
debug: libvulkan.so.1 loaded at 0x712c9580e000 - 0x712c958971b0
debug: vkEnumerateInstanceVersion = fn (*u32) callconv(.c) vk.Result@712c958417a0
General protection exception (no address available)
???:?:?: 0x712c954a47af in ??? (???)
Unwind information for `???:0x712c954a47af` was not available, trace may be incomplete
???:?:?: 0x712c954a964c in ??? (???)
???:?:?: 0x712c9583626e in ??? (???)
???:?:?: 0x712c95842461 in ??? (???)
???:?:?: 0x712c958608f8 in ??? (???)
???:?:?: 0x712c958417f0 in ??? (???)
/home/geemili/code/dlopen-mesa-with-zig/src/main.zig:16:46: 0x1049859 in main (dlopen-mesa-with-zig)
const result = vkEnumerateInstanceVersion(&version);
^
/home/geemili/code/zig/build-master/stage3/lib/zig/std/start.zig:656:37: 0x104277a in posixCallMainAndExit (dlopen-mesa-with-zig)
const result = root.main() catch |err| {
^
/home/geemili/code/zig/build-master/stage3/lib/zig/std/start.zig:271:5: 0x104232d in _start (dlopen-mesa-with-zig)
asm volatile (switch (native_arch) {
^
Running it in lldb we get some disassembly:
Process 450185 stopped
* thread #1, name = 'dlopen-mesa-wit', stop reason = signal SIGSEGV: invalid address (fault address: 0x0)
frame #0: 0x00007ffff7b847af
-> 0x7ffff7b847af: movq %rcx, %fs:(%rax)
0x7ffff7b847b3: addq $0x60, %rcx
0x7ffff7b847b7: movq %rcx, %rax
0x7ffff7b847ba: leaq 0x7f0(%rcx), %rdx
(lldb)
I don’t understand how thread local storage works at the moment, so I’ll have to come back to this. I probably also need to handle .tdata and .tbss.
I am wondering at this point if the system libc.so.6 could be replaced with a theoretical ziglibc. libvulkan.so.1 itself only uses a couple symbols:
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Though I guess the drivers that libvulkan.so.1 loads would probably rely on many more symbols.