Module Name: src
Committed By: riastradh
Date: Mon Jul 22 23:18:50 UTC 2024
Modified Files:
src/libexec/ld.elf_so/arch/aarch64: rtld_start.S
Log Message:
ld.elf_so aarch64/rtld_start.S: Sprinkle comments.
No functional change intended.
Prompted by PR lib/58154.
To generate a diff of this commit:
cvs rdiff -u -r1.5 -r1.6 src/libexec/ld.elf_so/arch/aarch64/rtld_start.S
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/libexec/ld.elf_so/arch/aarch64/rtld_start.S
diff -u src/libexec/ld.elf_so/arch/aarch64/rtld_start.S:1.5 src/libexec/ld.elf_so/arch/aarch64/rtld_start.S:1.6
--- src/libexec/ld.elf_so/arch/aarch64/rtld_start.S:1.5 Thu Mar 24 12:12:00 2022
+++ src/libexec/ld.elf_so/arch/aarch64/rtld_start.S Mon Jul 22 23:18:50 2024
@@ -1,4 +1,4 @@
-/* $NetBSD: rtld_start.S,v 1.5 2022/03/24 12:12:00 andvar Exp $ */
+/* $NetBSD: rtld_start.S,v 1.6 2024/07/22 23:18:50 riastradh Exp $ */
/*-
* Copyright (c) 2014 The NetBSD Foundation, Inc.
@@ -60,7 +60,7 @@
#include <machine/asm.h>
-RCSID("$NetBSD: rtld_start.S,v 1.5 2022/03/24 12:12:00 andvar Exp $")
+RCSID("$NetBSD: rtld_start.S,v 1.6 2024/07/22 23:18:50 riastradh Exp $")
/*
* void _rtld_start(void (*cleanup)(void), const Obj_Entry *obj,
@@ -146,87 +146,122 @@ ENTRY_NP(_rtld_bind_start)
END(_rtld_bind_start)
/*
- * struct rel_tlsdesc {
- * uint64_t resolver_fnc;
- * uint64_t resolver_arg;
+ * Entry points used by _rtld_tlsdesc_fill. They will be passed in x0
+ * a pointer to:
*
+ * struct rel_tlsdesc {
+ * uint64_t resolver_fnc;
+ * uint64_t resolver_arg;
+ * };
*
- * uint64_t _rtld_tlsdesc_static(struct rel_tlsdesc *);
+ * They are called with nonstandard calling convention and must
+ * preserve all registers except x0.
+ */
+
+/*
+ * uint64_t@x0
+ * _rtld_tlsdesc_static(struct rel_tlsdesc *rel_tlsdesc@x0);
+ *
+ * Resolver function for TLS symbols resolved at load time.
*
- * Resolver function for TLS symbols resolved at load time
+ * rel_tlsdesc->resolver_arg is the offset of the static
+ * thread-local storage region, relative to the start of the TCB.
+ *
+ * Nonstandard calling convention: Must preserve all registers
+ * except x0.
*/
ENTRY(_rtld_tlsdesc_static)
.cfi_startproc
- ldr x0, [x0, #8]
- ret
+ ldr x0, [x0, #8] /* x0 := tcboffset */
+ ret /* return x0 = tcboffset */
.cfi_endproc
END(_rtld_tlsdesc_static)
/*
- * uint64_t _rtld_tlsdesc_undef(void);
+ * uint64_t@x0
+ * _rtld_tlsdesc_undef(struct rel_tlsdesc *rel_tlsdesc@x0);
+ *
+ * Resolver function for weak and undefined TLS symbols.
*
- * Resolver function for weak and undefined TLS symbols
+ * rel_tlsdesc->resolver_arg is the Elf_Rela rela->r_addend.
+ *
+ * Nonstandard calling convention: Must preserve all registers
+ * except x0.
*/
ENTRY(_rtld_tlsdesc_undef)
.cfi_startproc
- str x1, [sp, #-16]!
+ str x1, [sp, #-16]! /* save x1 on stack */
.cfi_adjust_cfa_offset 16
- mrs x1, tpidr_el0
- ldr x0, [x0, #8]
- sub x0, x0, x1
+ mrs x1, tpidr_el0 /* x1 := current thread tcb */
+ ldr x0, [x0, #8] /* x0 := rela->r_addend */
+ sub x0, x0, x1 /* x0 := rela->r_addend - tcb */
- ldr x1, [sp], #16
- .cfi_adjust_cfa_offset -16
+ ldr x1, [sp], #16 /* restore x1 from stack */
+ .cfi_adjust_cfa_offset -16
.cfi_endproc
- ret
+ ret /* return x0 = rela->r_addend - tcb */
END(_rtld_tlsdesc_undef)
/*
- * uint64_t _rtld_tlsdesc_dynamic(struct rel_tlsdesc *);
+ * uint64_t@x0
+ * _rtld_tlsdesc_dynamic(struct rel_tlsdesc *tlsdesc@x0);
+ *
+ * Resolver function for TLS symbols from dlopen().
*
- * Resolver function for TLS symbols from dlopen()
+ * rel_tlsdesc->resolver_arg is a pointer to a struct tls_data
+ * object allocated during relocation.
+ *
+ * Nonstandard calling convention: Must preserve all registers
+ * except x0.
*/
ENTRY(_rtld_tlsdesc_dynamic)
.cfi_startproc
/* Save registers used in fast path */
- stp x1, x2, [sp, #(-2 * 16)]!
- stp x3, x4, [sp, #(1 * 16)]
+ stp x1, x2, [sp, #(-2 * 16)]!
+ stp x3, x4, [sp, #(1 * 16)]
.cfi_adjust_cfa_offset 2 * 16
.cfi_rel_offset x1, 0
.cfi_rel_offset x2, 8
.cfi_rel_offset x3, 16
.cfi_rel_offset x4, 24
- /* Test fastpath - inlined version of __tls_get_addr. */
+ /* Try for the fast path -- inlined version of __tls_get_addr. */
- ldr x1, [x0, #8] /* tlsdesc ptr */
- mrs x4, tpidr_el0
- ldr x0, [x4] /* DTV pointer (tcb->tcb_dtv) */
+ ldr x1, [x0, #8] /* x1 := tlsdesc (struct tls_data *) */
+ mrs x4, tpidr_el0 /* x4 := tcb */
+ ldr x0, [x4] /* x0 := dtv = tcb->tcb_dtv */
- ldr x3, [x0, #-8] /* DTV_MAX_INDEX(dtv) */
- ldr x2, [x1, #0] /* tlsdesc->td_tlsindex */
+ ldr x3, [x0, #-8] /* x3 := max = DTV_MAX_INDEX(dtv) */
+ ldr x2, [x1, #0] /* x2 := idx = tlsdesc->td_tlsindex */
cmp x2, x3
- b.lt 1f /* Slow path */
+ b.lt 1f /* Slow path if idx < max */
+ /* XXX PR lib/58154 */
+
+ ldr x3, [x0, x2, lsl #3] /* x3 := dtv[idx] */
+ cbz x3, 1f /* Slow path if dtv[idx] is null */
- ldr x3, [x0, x2, lsl #3] /* dtv[tlsdesc->td_tlsindex] */
- cbz x3, 1f
+ /*
+ * Fast path
+ *
+ * return (dtv[tlsdesc->td_tlsindex] + tlsdesc->td_tlsoffs - tcb)
+ */
+ ldr x2, [x1, #8] /* x2 := offs = tlsdesc->td_tlsoffs */
+ add x2, x2, x3 /* x2 := addr = dtv[idx] + offs */
+ sub x0, x2, x4 /* x0 := addr - tcb
- /* Return (dtv[tlsdesc->td_tlsindex] + tlsdesc->td_tlsoffs - tp) */
- ldr x2, [x1, #8] /* tlsdesc->td_tlsoffs */
- add x2, x2, x3
- sub x0, x2, x4
-
- /* Restore registers and return */
- ldp x3, x4, [sp, #(1 * 16)]
- ldp x1, x2, [sp], #(2 * 16)
- .cfi_adjust_cfa_offset -2 * 16
- ret
+ /* Restore fast path registers and return */
+ ldp x3, x4, [sp, #(1 * 16)]
+ ldp x1, x2, [sp], #(2 * 16)
+ .cfi_adjust_cfa_offset -2 * 16
+ ret /* return x0 = addr - tcb */
/*
* Slow path
- * return _rtld_tls_get_addr(tp, tlsdesc->td_tlsindex, tlsdesc->td_tlsoffs);
+ *
+ * return _rtld_tls_get_addr(tp, tlsdesc->td_tlsindex,
+ * tlsdesc->td_tlsoffs);
*
*/
1:
@@ -236,18 +271,18 @@ ENTRY(_rtld_tlsdesc_dynamic)
.cfi_rel_offset x29, 0
.cfi_rel_offset x30, 8
- stp x5, x6, [sp, #(1 * 16)]
- stp x7, x8, [sp, #(2 * 16)]
- stp x9, x10, [sp, #(3 * 16)]
+ stp x5, x6, [sp, #(1 * 16)]
+ stp x7, x8, [sp, #(2 * 16)]
+ stp x9, x10, [sp, #(3 * 16)]
stp x11, x12, [sp, #(4 * 16)]
stp x13, x14, [sp, #(5 * 16)]
stp x15, x16, [sp, #(6 * 16)]
stp x17, x18, [sp, #(7 * 16)]
- .cfi_rel_offset x5, 16
- .cfi_rel_offset x6, 24
- .cfi_rel_offset x7, 32
- .cfi_rel_offset x8, 40
- .cfi_rel_offset x9, 48
+ .cfi_rel_offset x5, 16
+ .cfi_rel_offset x6, 24
+ .cfi_rel_offset x7, 32
+ .cfi_rel_offset x8, 40
+ .cfi_rel_offset x9, 48
.cfi_rel_offset x10, 56
.cfi_rel_offset x11, 64
.cfi_rel_offset x12, 72
@@ -259,31 +294,32 @@ ENTRY(_rtld_tlsdesc_dynamic)
.cfi_rel_offset x18, 120
/* Find the tls offset */
- mov x0, x4 /* tp */
- mov x3, x1 /* tlsdesc ptr */
- ldr x1, [x3, #0] /* tlsdesc->td_tlsindex */
- ldr x2, [x3, #8] /* tlsdesc->td_tlsoffs */
- bl _rtld_tls_get_addr
- mrs x1, tpidr_el0
- sub x0, x0, x1
+ mov x0, x4 /* x0 := tcb */
+ mov x3, x1 /* x3 := tlsdesc */
+ ldr x1, [x3, #0] /* x1 := idx = tlsdesc->td_tlsindex */
+ ldr x2, [x3, #8] /* x2 := offs = tlsdesc->td_tlsoffs */
+ bl _rtld_tls_get_addr /* x0 := addr = _rtld_tls_get_addr(tcb,
+ * idx, offs) */
+ mrs x1, tpidr_el0 /* x1 := tcb */
+ sub x0, x0, x1 /* x0 := addr - tcb */
/* Restore slow path registers */
ldp x17, x18, [sp, #(7 * 16)]
ldp x15, x16, [sp, #(6 * 16)]
ldp x13, x14, [sp, #(5 * 16)]
ldp x11, x12, [sp, #(4 * 16)]
- ldp x9, x10, [sp, #(3 * 16)]
- ldp x7, x8, [sp, #(2 * 16)]
- ldp x5, x6, [sp, #(1 * 16)]
+ ldp x9, x10, [sp, #(3 * 16)]
+ ldp x7, x8, [sp, #(2 * 16)]
+ ldp x5, x6, [sp, #(1 * 16)]
ldp x29, x30, [sp], #(8 * 16)
- .cfi_adjust_cfa_offset -8 * 16
+ .cfi_adjust_cfa_offset -8 * 16
.cfi_restore x29
.cfi_restore x30
/* Restore fast path registers and return */
- ldp x3, x4, [sp, #16]
- ldp x1, x2, [sp], #(2 * 16)
+ ldp x3, x4, [sp, #16]
+ ldp x1, x2, [sp], #(2 * 16)
.cfi_adjust_cfa_offset -2 * 16
.cfi_endproc
- ret
+ ret /* return x0 = addr - tcb */
END(_rtld_tlsdesc_dynamic)
