From 90dad97fc07f049383903a166631e2c257f9b8c1 Mon Sep 17 00:00:00 2001
From: Kacper <kacper@mail.openlinux.dev>
Date: Tue, 16 Dec 2025 17:02:05 +0100
Subject: Add support for TLS in the libc

---
 lib/libc/internal/init/tls.c | 76 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 lib/libc/internal/init/tls.c

(limited to 'lib/libc/internal/init/tls.c')

diff --git a/lib/libc/internal/init/tls.c b/lib/libc/internal/init/tls.c
new file mode 100644
index 00000000..f6ccde35
--- /dev/null
+++ b/lib/libc/internal/init/tls.c
@@ -0,0 +1,76 @@
+#include <__thread.h>
+#include <asm/prctl.h>
+#include <elf.h>
+#include <libc.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <syscall.h>
+
+#define ALIGN_DOWN(x, a) ((x) & ~((a) - 1))
+#define ALIGN_UP(x, a)	 (((x) + (a) - 1) & ~((a) - 1))
+
+static struct tls __libc_tls = { 0 };
+static struct __thread_self __libc_thread;
+volatile int __libc_tid;
+
+void __init_tls(void)
+{
+	int r;
+	void *mem;
+	size_t base;
+	unsigned char *p;
+	Elf64_Phdr *tls_phdr;
+	struct __thread_self *thrd;
+
+	base = 0;
+	tls_phdr = 0;
+	p = (void *)__libc.auxv[AT_PHDR];
+	for (size_t n = __libc.auxv[AT_PHNUM]; n > 0; n--, p += __libc.auxv[AT_PHENT]) {
+		Elf64_Phdr *phdr = (Elf64_Phdr *)p;
+
+		if (phdr->p_type == PT_PHDR) {
+			base = __libc.auxv[AT_PHDR] - phdr->p_vaddr;
+		} else if (phdr->p_type == PT_TLS) {
+			tls_phdr = phdr;
+		}
+	}
+
+	if (tls_phdr) {
+		__libc_tls.data = (void *)(base + tls_phdr->p_vaddr);
+		__libc_tls.length = tls_phdr->p_filesz;
+		__libc_tls.size = tls_phdr->p_memsz;
+		__libc_tls.align = tls_phdr->p_align;
+	}
+
+	if (__libc_tls.size != 0) {
+		void *tls_mem;
+		size_t tls_size = __libc_tls.size + sizeof(struct __thread_self);
+		tls_size = (tls_size + __libc_tls.align - 1) & ~(__libc_tls.align - 1);
+
+		mem = mmap(0, tls_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+		panic_if(mem == MAP_FAILED, "mmap failed");
+
+		__libc.tls.base = mem;
+		__libc.tls.size = tls_size;
+
+		thrd = (struct __thread_self *)mem;
+		tls_mem = (unsigned char *)mem + sizeof(struct __thread_self);
+
+		if (tls_phdr->p_filesz > 0) {
+			memcpy(tls_mem, (void *)tls_phdr->p_vaddr, tls_phdr->p_filesz);
+			memset(tls_mem + tls_phdr->p_filesz, 0, tls_phdr->p_memsz - tls_phdr->p_filesz);
+		} else {
+			memset(tls_mem, 0, tls_phdr->p_memsz);
+		}
+
+		r = syscall(arch_prctl, ARCH_SET_FS, mem + sizeof(struct __thread_self));
+		panic_if(r < 0, "arch_prctl(SET_FS) failed");
+	} else {
+		__libc.tls.base = NULL;
+		thrd = &__libc_thread;
+	}
+
+	r = syscall(set_tid_address, &__libc_tid);
+	panic_if(r < 0, "set_tid_address failed");
+	thrd->tid = r;
+}
-- 
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