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Merged
jserv merged 1 commit into from
May 10, 2026
Merged

Add musl libc integration with ARM FDPIC dynamic linking #19

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498 changes: 483 additions & 15 deletions build.sh
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4 changes: 2 additions & 2 deletions configs/busybox-1.37.0.config
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Original file line number Diff line number Diff line change
Expand Up @@ -1140,8 +1140,8 @@ CONFIG_BASH_IS_NONE=y
# CONFIG_CTTYHACK is not set
CONFIG_HUSH=y
CONFIG_SHELL_HUSH=y
CONFIG_HUSH_BASH_COMPAT=y
CONFIG_HUSH_BRACE_EXPANSION=y
# CONFIG_HUSH_BASH_COMPAT is not set
# CONFIG_HUSH_BRACE_EXPANSION is not set
# CONFIG_HUSH_BASH_SOURCE_CURDIR is not set
CONFIG_HUSH_LINENO_VAR=y
CONFIG_HUSH_INTERACTIVE=y
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16 changes: 16 additions & 0 deletions configs/musl-smoke-workload.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
# label|command|expected regex
#
# Musl-specific runtime smoke layered on top of the generic BusyBox workload.
# Keep commands restricted to applets already enabled in configs/busybox-1.37.0.config.
loader-path|busybox ls -l /lib/ld-musl-arm-fdpic.so.1 >/dev/null && busybox echo ok|ok
libc-path|busybox ls /lib/libc.so >/dev/null && busybox echo ok|ok
shell-link|busybox ls -l /bin/sh >/dev/null && busybox echo ok|ok
uname|busybox uname -s >/dev/null && busybox echo ok|ok
list-bin|busybox ls /bin >/dev/null && busybox echo ok|ok
proc-version|busybox cat /proc/version >/dev/null && busybox echo ok|ok
proc-self-stat|busybox cat /proc/self/stat >/dev/null && busybox echo ok|ok
create-file|busybox sh -c 'busybox echo alpha >/tmp/musl-file && busybox cat /tmp/musl-file >/dev/null' && busybox echo ok|ok
copy-file|busybox sh -c 'busybox cp /bin/busybox /tmp/musl-copy && busybox ls /tmp/musl-copy >/dev/null' && busybox echo ok|ok
rename-file|busybox sh -c 'busybox mv /tmp/musl-file /tmp/musl-file-renamed && busybox cat /tmp/musl-file-renamed >/dev/null' && busybox echo ok|ok
hardlink-file|busybox sh -c 'busybox ln /tmp/musl-file-renamed /tmp/musl-file-link && busybox ls /tmp/musl-file-link >/dev/null' && busybox echo ok|ok
cleanup-tmp|busybox sh -c 'busybox rm -f /tmp/musl-file-renamed /tmp/musl-file-link /tmp/musl-copy' && busybox echo ok|ok
162 changes: 162 additions & 0 deletions patches/0024-musl-arm-fdpic-dynamic-linking.patch
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Original file line number Diff line number Diff line change
@@ -0,0 +1,162 @@
diff -uNr musl-patch-old/arch/arm/crt_arch.h musl-patch-new/arch/arm/crt_arch.h
--- musl-patch-old/arch/arm/crt_arch.h 2026-05-10 03:00:12.907245512 +0800
+++ musl-patch-new/arch/arm/crt_arch.h 2026-05-10 03:00:12.907745845 +0800
@@ -1,3 +1,61 @@
+#ifdef __FDPIC__
+
+#if !defined(__thumb__) || defined(__thumb2__)
+__asm__(
+".text \n"
+".global " START " \n"
+".type " START ",%function \n"
+".thumb \n"
+".thumb_func \n"
+START ": \n"
+#ifdef SHARED
+" mov r4, sp \n"
+" sub r5, pc, #4 \n"
+" ldr r1, 1f \n"
+" add r1, r1, r5 \n"
+" ldr r2, 2f \n"
+" add r2, r2, r5 \n"
+" movs r0, r8 \n"
+" it eq \n"
+" moveq r0, r7 \n"
+" push {r7, r8, r9, r10} \n"
+" bl __fdpic_fixup \n"
+" pop {r7, r8, r9, r10} \n"
+" push {r7, r8} \n"
+" mov r1, r9 \n"
+" mov r9, r0 \n"
+" mov r0, r4 \n"
+" bl " START "_c \n"
+".align 2 \n"
+"1: .word __ROFIXUP_LIST__ - " START " \n"
+"2: .word __ROFIXUP_END__ - " START " \n"
+#else
+" sub r4, pc, #4 \n"
+" ldr r1, 1f \n"
+" add r1, r1, r4 \n"
+" ldr r2, 2f \n"
+" add r2, r2, r4 \n"
+" mov r0, r7 \n"
+" bl __self_reloc \n"
+" mov r9, r0 \n"
+" mov r0, sp \n"
+" movs r3, #0 \n"
+" mov fp, r3 \n"
+" bl " START "_c \n"
+".align 2 \n"
+"1: .word __ROFIXUP_LIST__ - " START " \n"
+"2: .word __ROFIXUP_END__ - " START " \n"
+#endif
+);
+
+#include "fdpic_crt.h"
+
+#else
+#error ARM FDPIC requires Thumb-2 or ARM mode support in crt startup
+#endif
+
+#else
+
__asm__(
".text \n"
".global " START " \n"
@@ -16,3 +74,5 @@
".align 2 \n"
"1: .word _DYNAMIC-2b \n"
);
+
+#endif
diff -uNr musl-patch-old/arch/arm/pthread_arch.h musl-patch-new/arch/arm/pthread_arch.h
--- musl-patch-old/arch/arm/pthread_arch.h 2026-05-10 03:00:12.907347137 +0800
+++ musl-patch-new/arch/arm/pthread_arch.h 2026-05-10 03:00:12.907821595 +0800
@@ -30,3 +30,8 @@
#define GAP_ABOVE_TP 8

#define MC_PC arm_pc
+
+#ifdef __FDPIC__
+#define MC_GOT arm_r9
+#define CANCEL_GOT (*(uintptr_t *)((char *)__syscall_cp_asm+sizeof(uintptr_t)))
+#endif
diff -uNr musl-patch-old/arch/arm/reloc.h musl-patch-new/arch/arm/reloc.h
--- musl-patch-old/arch/arm/reloc.h 2026-05-10 03:00:12.907433137 +0800
+++ musl-patch-new/arch/arm/reloc.h 2026-05-10 03:00:12.907897512 +0800
@@ -10,7 +10,13 @@
#define FP_SUFFIX ""
#endif

-#define LDSO_ARCH "arm" ENDIAN_SUFFIX FP_SUFFIX
+#if __FDPIC__
+#define ABI_SUFFIX "-fdpic"
+#else
+#define ABI_SUFFIX ""
+#endif
+
+#define LDSO_ARCH "arm" ENDIAN_SUFFIX FP_SUFFIX ABI_SUFFIX

#define NO_LEGACY_INITFINI

@@ -28,5 +34,41 @@

#define TLSDESC_BACKWARDS 1

+#if __FDPIC__
+#ifndef R_ARM_FUNCDESC
+#define R_ARM_FUNCDESC 163
+#endif
+#ifndef R_ARM_FUNCDESC_VALUE
+#define R_ARM_FUNCDESC_VALUE 164
+#endif
+#define REL_FUNCDESC R_ARM_FUNCDESC
+#define REL_FUNCDESC_VAL R_ARM_FUNCDESC_VALUE
+#define DL_FDPIC 1
+#define DL_NOMMU_SUPPORT 1
+#define FDPIC_IS_RELATIVE(x,s) ( \
+ (R_TYPE(x) == REL_RELATIVE) || \
+ ((((R_TYPE(x) == REL_FUNCDESC_VAL) || \
+ (R_TYPE(x) == REL_SYMBOLIC)) && \
+ (((s)[R_SYM(x)].st_info & 0xf) == STT_SECTION))) )
+#define CRTJMP(pc,sp) do { \
+ register size_t r7 __asm__("r7") = ((size_t *)(sp))[-2]; \
+ __asm__ __volatile__( \
+ "mov sp,%1 ; bx %0" \
+ : \
+ : "r"(pc), "r"(sp), "r"(r7) \
+ : "memory"); \
+} while(0)
+#define GETFUNCSYM(fp, sym, got) __asm__ ( \
+ "ldr %0, 1f \n" \
+ "ldr %0, [%1, %0] \n" \
+ "add %0, %0, %1 \n" \
+ "b 2f \n" \
+ ".align 2 \n" \
+ "1: .word " #sym "(GOTFUNCDESC) \n" \
+ "2: \n" \
+ : "=&r"(*fp) : "r"(got) : "memory" )
+#else
+
#define CRTJMP(pc,sp) __asm__ __volatile__( \
"mov sp,%1 ; bx %0" : : "r"(pc), "r"(sp) : "memory" )
+#endif
diff -uNr musl-patch-old/src/internal/dynlink.h musl-patch-new/src/internal/dynlink.h
--- musl-patch-old/src/internal/dynlink.h 2026-05-10 03:00:12.907595304 +0800
+++ musl-patch-new/src/internal/dynlink.h 2026-05-10 03:00:12.908054428 +0800
@@ -82,11 +82,14 @@
(R_TYPE(x) == REL_RELATIVE) || \
(R_TYPE(x) == REL_SYM_OR_REL && !R_SYM(x)) )
#else
-#define IS_RELATIVE(x,s) ( ( \
+#ifndef FDPIC_IS_RELATIVE
+#define FDPIC_IS_RELATIVE(x,s) ( ( \
(R_TYPE(x) == REL_FUNCDESC_VAL) || \
(R_TYPE(x) == REL_SYMBOLIC) ) \
&& (((s)[R_SYM(x)].st_info & 0xf) == STT_SECTION) )
#endif
+#define IS_RELATIVE(x,s) FDPIC_IS_RELATIVE(x,s)
+#endif

#ifndef NEED_MIPS_GOT_RELOCS
#define NEED_MIPS_GOT_RELOCS 0
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