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From 3bc16e0b58704b8c3bd596b23d907516c7cc2493 Mon Sep 17 00:00:00 2001
From: Clint Bland <bland.cr@gmail.com>
Date: Thu, 14 Mar 2019 02:19:16 +0000
Subject: [PATCH] PPC: Call libm helpers via private GOT instead of the PLT
A bl sym@plt call emitted by the VM assembler produces an
R_PPC_PLTREL24 relocation with addend 0, which forces the linker to
use BSS-PLT for the entire link. GCC 12 and newer emit inline-PLT
relocations (R_PPC_PLTSEQ, R_PPC_PLTCALL, R_PPC_PLT16_*) that have no
BSS-PLT equivalent, so linking libluajit.so fails outright:
ld: bss-plt forced due to lj_vm.o
ld: crtstuff.c:(.text+0x46): R_PPC_PLT16_HA relocation unsupported
for bss-plt
Route these calls through a private GOT stored in GG_State, the way
the MIPS port already does. No PLT relocation is emitted, the linker
selects secure-PLT and the link succeeds.
Originally submitted upstream as LuaJIT/LuaJIT#486, against 2.0 and
addressing LuaJIT/LuaJIT#481, and closed without being merged. OpenWrt
has carried it for the upstream luajit package as 060-ppc-musl.patch
since 2019, extended with the soft-float helpers the 2.1 branch needs
in the GOT. Adapted here for luajit2 and verified on OpenWrt.
Tested on Turris 1.x (e500v2, 32-bit big-endian, musl, soft-float)
with BUILDMODE=dynamic. No R_PPC_PLTREL24 relocations remain, and the
resulting binary runs correctly, including all libm calls routed
through the new GOT. The previously produced dynamic binary crashed
during startup.
Co-authored-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
---
src/lj_dispatch.c | 11 ++++++++++-
src/lj_dispatch.h | 32 +++++++++++++++++++++++++++++++-
src/vm_ppc.dasc | 12 +++++++++++-
3 files changed, 52 insertions(+), 3 deletions(-)
--- a/src/lj_dispatch.c
+++ b/src/lj_dispatch.c
@@ -56,6 +56,15 @@ static const ASMFunction dispatch_got[]
#undef GOTFUNC
#endif
+#if LJ_TARGET_PPC && LJ_32
+#include <math.h>
+#define GOTFUNC(name) (ASMFunction)name,
+static const ASMFunction dispatch_got[] = {
+ GOTDEF(GOTFUNC)
+};
+#undef GOTFUNC
+#endif
+
/* Initialize instruction dispatch table and hot counters. */
void lj_dispatch_init(GG_State *GG)
{
@@ -76,7 +85,7 @@ void lj_dispatch_init(GG_State *GG)
GG->g.bc_cfunc_ext = GG->g.bc_cfunc_int = BCINS_AD(BC_FUNCC, LUA_MINSTACK, 0);
for (i = 0; i < GG_NUM_ASMFF; i++)
GG->bcff[i] = BCINS_AD(BC__MAX+i, 0, 0);
-#if LJ_TARGET_MIPS
+#if LJ_TARGET_MIPS || (LJ_TARGET_PPC && LJ_32)
memcpy(GG->got, dispatch_got, LJ_GOT__MAX*sizeof(ASMFunction *));
#endif
}
--- a/src/lj_dispatch.h
+++ b/src/lj_dispatch.h
@@ -66,6 +66,36 @@ GOTDEF(GOTENUM)
};
#endif
+#if LJ_TARGET_PPC && LJ_32
+/* Call libm/libgcc helpers via our own GOT instead of the PLT. A PLT call
+** from the VM assembler forces the obsolete BSS-PLT for the whole link,
+** which fails against secure-PLT objects emitted by GCC 12 and newer.
+*/
+#if LJ_SOFTFP
+#ifndef _LJ_IRCALL_H
+extern double __ledf2(double a, double b);
+extern double __adddf3(double a, double b);
+extern double __subdf3(double a, double b);
+extern double __muldf3(double a, double b);
+extern double __divdf3(double a, double b);
+#endif
+#define SFGOTDEF(_) _(__ledf2) _(__adddf3) _(__subdf3) _(__muldf3) _(__divdf3)
+#else
+#define SFGOTDEF(_)
+#endif
+#define GOTDEF(_) \
+ _(floor) _(ceil) _(trunc) _(log) _(log10) _(exp) _(sin) _(cos) _(tan) \
+ _(asin) _(acos) _(atan) _(sinh) _(cosh) _(tanh) _(frexp) _(modf) _(atan2) \
+ _(pow) _(fmod) _(ldexp) _(sqrt) SFGOTDEF(_)
+
+enum {
+#define GOTENUM(name) LJ_GOT_##name,
+GOTDEF(GOTENUM)
+#undef GOTENUM
+ LJ_GOT__MAX
+};
+#endif
+
/* Type of hot counter. Must match the code in the assembler VM. */
/* 16 bits are sufficient. Only 0.0015% overhead with maximum slot penalty. */
typedef uint16_t HotCount;
@@ -93,7 +123,7 @@ typedef struct GG_State {
/* Make g reachable via K12 encoded DISPATCH-relative addressing. */
uint8_t align1[(16-sizeof(global_State))&15];
#endif
-#if LJ_TARGET_MIPS
+#if LJ_TARGET_MIPS || (LJ_TARGET_PPC && LJ_32)
ASMFunction got[LJ_GOT__MAX]; /* Global offset table. */
#endif
#if LJ_HASJIT
--- a/src/vm_ppc.dasc
+++ b/src/vm_ppc.dasc
@@ -50,7 +50,13 @@
|.macro blex, target; bl extern target; nop; .endmacro
|.macro .toc, a, b; a, b; .endmacro
|.else
-|.macro blex, target; bl extern target@plt; .endmacro
+|// Call via our own GOT to avoid PLT relocations, which force the obsolete
+|// BSS-PLT on PPC32 and break linking against secure-PLT objects.
+|.macro blex, target
+| lwz TMP0, DISPATCH_GOT(target)(DISPATCH)
+| mtctr TMP0
+| bctrl
+|.endmacro
|.macro .toc, a, b; .endmacro
|.endif
|.if OPD
@@ -577,6 +583,10 @@
|// Assumes DISPATCH is relative to GL.
#define DISPATCH_GL(field) (GG_DISP2G + (int)offsetof(global_State, field))
#define DISPATCH_J(field) (GG_DISP2J + (int)offsetof(jit_State, field))
+#if LJ_TARGET_PPC && LJ_32
+#define GG_DISP2GOT (GG_OFS(got) - GG_OFS(dispatch))
+#define DISPATCH_GOT(name) (GG_DISP2GOT + 4*LJ_GOT_##name)
+#endif
|
#define PC2PROTO(field) ((int)offsetof(GCproto, field)-(int)sizeof(GCproto))
|
|
