Changeset b27ae65a in mainline for uspace/lib/c/generic/thread/tls.c

Timestamp:

2025-01-27T12:45:12Z (11 days ago)

Author:

GitHub <noreply@…>

Branches:

master

Children:

97116a2

Parents:

eff458d

git-author:

Matěj Volf <mat.volfik@…> (2025-01-27 12:45:12)

git-committer:

GitHub <noreply@…> (2025-01-27 12:45:12)

Message:

fix calculation of TLS size for main fibril (#240)

• explain why tcb_t is added at the end of tls allocation

• fix calculation of TLS size for main fibril

Before this patch, _tcb_data_offset always used progsymbols.elfstart. However,
that is wrong when it is being called from the loader server!! Now we pass to it
a pointer to the correct ELF, falling back to elfstart in the public tls_get call.

(debugging this was quite an ordeal and took me like 5 hours, thanks for asking ('

• a few comments for TLS allocation

File:

• uspace/lib/c/generic/thread/tls.c (modified) (4 diffs)

uspace/lib/c/generic/thread/tls.c

@@ -59 +59 @@
 #endif
 
-static ptrdiff_t _tcb_data_offset(void)
+static ptrdiff_t _tcb_data_offset(const void* elf)
 {
         const elf_segment_header_t *tls =
-            elf_get_phdr(__progsymbols.elfstart, PT_TLS);
+            elf_get_phdr(elf, PT_TLS);
 
         size_t tls_align = tls ? tls->p_align : 1;
@@ -80 +80 @@
         assert(runtime_env == NULL);
 #endif
-        return (uint8_t *)__tcb_get() + _tcb_data_offset();
+        return (uint8_t *)__tcb_get() + _tcb_data_offset(__progsymbols.elfstart);
 }
 
 static tcb_t *tls_make_generic(const void *elf, void *(*alloc)(size_t, size_t))
 {
+        /*
+         * See also rtld/module.c -> modules_process_tls(), where we have less
+         * messy code for the dynamic-linking version of this.
+         */
         assert(!elf_get_phdr(elf, PT_DYNAMIC));
 #ifdef CONFIG_RTLD
@@ -100 +104 @@
         assert(tls_align <= PAGE_SIZE);
 
+        /*
+         * FIXME: the calculation of alloc_size shouldn't include the alignment
+         * of tcb_t (at least in Variant II)
+         * See https://github.com/HelenOS/helenos/pull/240/files/4ef27ebf98a0656e09889b7d00efdec03343f1aa#r1929592924
+         * (you will also need to fix _tcb_data_offset)
+         */
+
 #ifdef CONFIG_TLS_VARIANT_1
         size_t alloc_size =
@@ -114 +125 @@
 #ifdef CONFIG_TLS_VARIANT_1
         tcb_t *tcb = area;
-        uint8_t *data = (uint8_t *)tcb + _tcb_data_offset();
+        uint8_t *data = (uint8_t *)tcb + _tcb_data_offset(elf);
         memset(tcb, 0, sizeof(*tcb));
 #else
         uint8_t *data = area;
-        tcb_t *tcb = (tcb_t *) (data - _tcb_data_offset());
+        tcb_t *tcb = (tcb_t *) (data - _tcb_data_offset(elf));
         memset(tcb, 0, sizeof(tcb_t));
         tcb->self = tcb;