diff mbox series

[pushed] libffi: Fix X86 32b Darwin build and EH frames.

Message ID 20221221130901.39779-1-iain@sandoe.co.uk
State Committed
Headers
Series [pushed] libffi: Fix X86 32b Darwin build and EH frames. |

Commit Message

Iain Sandoe Dec. 21, 2022, 1:09 p.m. UTC 
  The addition of rust has pulled in libffi as a target library for Darwin.
This fails to bootstrap on some versions of i686-darwin and has build-time
diagnostics on all.  The EH is also invalid and those tests fail.

Note that X86 Darwin is not listed as supported upstream.
However I have made a pull request with this patch and confirmed that the
library builds on 
 i686-darwin9 ... darwin17 with recent GCC
 i686-darwin11 ... darwin17 with xcode clang.
 
 The testsuite is not too happy, but this patch does not attempt to
 address anything other than build failures (it happens to fix the EH
 tests as a by product).
 
 Tested on i686-darwin9-17, x86_64-linux-gnu (with a 32b multilib) and
 x86_64 darwin21, pushed to master, thanks,
 Iain

--- 8< ---

This addresses a number of issues in the X86 Darwin 32b port for libffi.

1. The pic symbol stubs are weak definitions; the correct section placement
   for these depends on the linker version in use.  We do not have access
   to that information, but we can use the target OS version (assumes that
   the user has installed the latest version of xcode available).
   When a coalesced section is in use (OS versions earlier than Darwin12 /
   OSX 10.8), its name must differ from  __TEXT,__text since otherwise that
   would correspond to altering the attributes of the .text section (which
   produces a diagnostic from the assembler).
   Here we use __TEXT, __textcoal_nt for this which is what GCC emits for
   these stubs.
   For later versions than Darwin 12 (OS X 10.8) we can place the stubs in
   the .text section (if we do not we get a diagnostic from clang -cc1as
   saying that the use of coalesced sections for this is deprecated).

2. The EH frame is specified manually, since there is no support for .cfi_
   directives in 'cctools' assemblers.  The implementation needs to provide
   offsets for CFA advance, code size and to the CIE as signed values
   rather than relocations. However the cctools assembler will produce a
   relocation for expressions like ' .long Lxx-Lyy' which then leads to a
   link-time error.  We correct this by forming the offset values using
   ' .set' directives and then assigning the results of them.

3. The register numbering used by m32 X86 Darwin EH frames is not the same
   as the DWARF debug numbering (the Frame and Stack pointer numbers are
   swapped).

4. The FDE address encoding used by the system tools is '0x10' (PCrel + abs)
   where the value provided was PCrel + sdata4.

5. GCC does not use compact unwind at present, and it was not implemented
   until Darwin10 / OSX 10.6.  There were some issues with function location
   in 10.6 so that the solution here suppresses emitting the compact unwind
   section until Darwin11 / OSX 10.7.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

libffi/ChangeLog:

	* src/x86/sysv.S (COMDAT): Amend section use for Darwin, accounting
	cases where coalesced is needed. (eh_frame): Rework to avoid relocs
	that cause builf fails on earlier Darwin.  Adjust register numbers
	to account for X86 m32 Darwin differences between EH and debug.
---
 libffi/src/x86/sysv.S | 121 +++++++++++++++++++++++++++++-------------
 1 file changed, 83 insertions(+), 38 deletions(-)
diff mbox series

Patch

diff --git a/libffi/src/x86/sysv.S b/libffi/src/x86/sysv.S
index 7110f02f5f3..c7a0fb51b48 100644
--- a/libffi/src/x86/sysv.S
+++ b/libffi/src/x86/sysv.S
@@ -888,10 +888,27 @@  ENDF(C(ffi_closure_raw_THISCALL))
 #endif /* !FFI_NO_RAW_API */
 
 #ifdef X86_DARWIN
-# define COMDAT(X)							\
-        .section __TEXT,__text,coalesced,pure_instructions;		\
+/* The linker in use on earlier Darwin needs weak definitions to be
+   placed in a coalesced section.  That section should not be called
+   __TEXT,__text since that would be re-defining the attributes of the
+   .text section (which is an error for earlier tools). Here we use
+   '__textcoal_nt' which is what GCC emits for this.
+   Later linker versions are happy to use a normal section and, after
+   Darwin12 / OSX 10.8, the tools warn that using coalesced sections
+   for this is deprecated so we must switch to avoid build fails and/or
+   deprecation warnings.  */
+# if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&		\
+   __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 1080
+#  define COMDAT(X)							\
+        .section __TEXT,__textcoal_nt,coalesced,pure_instructions;	\
+        .weak_definition X;						\
+        FFI_HIDDEN(X)
+# else
+#  define COMDAT(X)							\
+        .text;								\
         .weak_definition X;						\
         FFI_HIDDEN(X)
+# endif
 #elif defined __ELF__ && !(defined(__sun__) && defined(__svr4__))
 # define COMDAT(X)							\
 	.section .text.X,"axG",@progbits,X,comdat;			\
@@ -916,7 +933,37 @@  ENDF(C(__x86.get_pc_thunk.dx))
 #endif /* DARWIN || HIDDEN */
 #endif /* __PIC__ */
 
-/* Sadly, OSX cctools-as doesn't understand .cfi directives at all.  */
+/* Sadly, OSX cctools-as does not understand .cfi directives at all so
+   we build an eh frame by hand.  */
+
+#ifdef __APPLE__
+/* The cctools assembler will try to make a difference between two local
+   symbols into a relocation against, which will not work in the eh (produces
+   link-time fails).
+   To avoid this, we compute the symbol difference with a .set directive and
+   then substitute this value.  */
+# define LEN(N, P)	.set Llen$N$P,L(N)-L(P); .long Llen$N$P
+/* Note, this assume DW_CFA_advance_loc1 fits into 7 bits.  */
+# define ADV(N, P)	.set Ladv$N$P,L(N)-L(P); .byte 2, Ladv$N$P
+/* For historical reasons, the EH reg numbers for SP and FP are swapped from
+   the DWARF ones for 32b Darwin.  */
+# define SP 5
+# define FP 4
+# define ENC 0x10
+#else
+# define LEN(N, P)	.long L(N)-L(P)
+/* Assume DW_CFA_advance_loc1 fits.  */
+# define ADV(N, P)	.byte 2, L(N)-L(P)
+# define SP 4
+# define FP 5
+# define ENC 0x1b
+#endif
+
+#ifdef HAVE_AS_X86_PCREL
+# define PCREL(X)	X-.
+#else
+# define PCREL(X)	X@rel
+#endif
 
 #ifdef __APPLE__
 .section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support
@@ -928,17 +975,11 @@  EHFrame0:
 #else
 .section .eh_frame,EH_FRAME_FLAGS,@progbits
 #endif
-
-#ifdef HAVE_AS_X86_PCREL
-# define PCREL(X)	X - .
-#else
-# define PCREL(X)	X@rel
+#ifndef __APPLE__
+/* EH sections are already suitably aligned on Darwin.  */
+	.balign 4
 #endif
 
-/* Simplify advancing between labels.  Assume DW_CFA_advance_loc1 fits.  */
-#define ADV(N, P)	.byte 2, L(N)-L(P)
-
-	.balign 4
 L(CIE):
 	.set	L(set0),L(ECIE)-L(SCIE)
 	.long	L(set0)			/* CIE Length */
@@ -950,8 +991,8 @@  L(SCIE):
 	.byte	0x7c			/* CIE Data Alignment Factor */
 	.byte	0x8			/* CIE RA Column */
 	.byte	1			/* Augmentation size */
-	.byte	0x1b			/* FDE Encoding (pcrel sdata4) */
-	.byte	0xc, 4, 4		/* DW_CFA_def_cfa, %esp offset 4 */
+	.byte	ENC			/* FDE Encoding (pcrel abs/4byte) */
+	.byte	0xc, SP, 4		/* DW_CFA_def_cfa, %esp offset 4 */
 	.byte	0x80+8, 1		/* DW_CFA_offset, %eip offset 1*-4 */
 	.balign 4
 L(ECIE):
@@ -959,20 +1000,20 @@  L(ECIE):
 	.set	L(set1),L(EFDE1)-L(SFDE1)
 	.long	L(set1)			/* FDE Length */
 L(SFDE1):
-	.long	L(SFDE1)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE1, CIE)			/* FDE CIE offset */
 	.long	PCREL(L(UW0))		/* Initial location */
-	.long	L(UW5)-L(UW0)		/* Address range */
+	LEN(UW5, UW0)			/* Address range */
 	.byte	0			/* Augmentation size */
 	ADV(UW1, UW0)
-	.byte	0xc, 5, 8		/* DW_CFA_def_cfa, %ebp 8 */
-	.byte	0x80+5, 2		/* DW_CFA_offset, %ebp 2*-4 */
+	.byte	0xc, FP, 8		/* DW_CFA_def_cfa, %ebp 8 */
+	.byte	0x80+FP, 2		/* DW_CFA_offset, %ebp 2*-4 */
 	ADV(UW2, UW1)
 	.byte	0x80+3, 0		/* DW_CFA_offset, %ebx 0*-4 */
 	ADV(UW3, UW2)
 	.byte	0xa			/* DW_CFA_remember_state */
-	.byte	0xc, 4, 4		/* DW_CFA_def_cfa, %esp 4 */
+	.byte	0xc, SP, 4		/* DW_CFA_def_cfa, %esp 4 */
 	.byte	0xc0+3			/* DW_CFA_restore, %ebx */
-	.byte	0xc0+5			/* DW_CFA_restore, %ebp */
+	.byte	0xc0+FP			/* DW_CFA_restore, %ebp */
 	ADV(UW4, UW3)
 	.byte	0xb			/* DW_CFA_restore_state */
 	.balign	4
@@ -981,9 +1022,9 @@  L(EFDE1):
 	.set	L(set2),L(EFDE2)-L(SFDE2)
 	.long	L(set2)			/* FDE Length */
 L(SFDE2):
-	.long	L(SFDE2)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE2, CIE)			/* FDE CIE offset */
 	.long	PCREL(L(UW6))		/* Initial location */
-	.long	L(UW8)-L(UW6)		/* Address range */
+	LEN(UW8,UW6)			/* Address range */
 	.byte	0			/* Augmentation size */
 	ADV(UW7, UW6)
 	.byte	0xe, closure_FS+4	/* DW_CFA_def_cfa_offset */
@@ -993,9 +1034,9 @@  L(EFDE2):
 	.set	L(set3),L(EFDE3)-L(SFDE3)
 	.long	L(set3)			/* FDE Length */
 L(SFDE3):
-	.long	L(SFDE3)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE3, CIE)			/* FDE CIE offset */
 	.long	PCREL(L(UW9))		/* Initial location */
-	.long	L(UW11)-L(UW9)		/* Address range */
+	LEN(UW11, UW9)			/* Address range */
 	.byte	0			/* Augmentation size */
 	ADV(UW10, UW9)
 	.byte	0xe, closure_FS+4	/* DW_CFA_def_cfa_offset */
@@ -1005,9 +1046,9 @@  L(EFDE3):
 	.set	L(set4),L(EFDE4)-L(SFDE4)
 	.long	L(set4)			/* FDE Length */
 L(SFDE4):
-	.long	L(SFDE4)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE4, CIE)		/* FDE CIE offset */
 	.long	PCREL(L(UW12))		/* Initial location */
-	.long	L(UW20)-L(UW12)		/* Address range */
+	LEN(UW20, UW12)			/* Address range */
 	.byte	0			/* Augmentation size */
 	ADV(UW13, UW12)
 	.byte	0xe, closure_FS+4	/* DW_CFA_def_cfa_offset */
@@ -1033,9 +1074,9 @@  L(EFDE4):
 	.set	L(set5),L(EFDE5)-L(SFDE5)
 	.long	L(set5)			/* FDE Length */
 L(SFDE5):
-	.long	L(SFDE5)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE5, CIE)			/* FDE CIE offset */
 	.long	PCREL(L(UW21))		/* Initial location */
-	.long	L(UW23)-L(UW21)		/* Address range */
+	LEN(UW23, UW21)			/* Address range */
 	.byte	0			/* Augmentation size */
 	ADV(UW22, UW21)
 	.byte	0xe, closure_FS+4	/* DW_CFA_def_cfa_offset */
@@ -1045,9 +1086,9 @@  L(EFDE5):
 	.set	L(set6),L(EFDE6)-L(SFDE6)
 	.long	L(set6)			/* FDE Length */
 L(SFDE6):
-	.long	L(SFDE6)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE6, CIE)			/* FDE CIE offset */
 	.long	PCREL(L(UW24))		/* Initial location */
-	.long	L(UW26)-L(UW24)		/* Address range */
+	LEN(UW26, UW24)			/* Address range */
 	.byte	0			/* Augmentation size */
 	.byte	0xe, 8			/* DW_CFA_def_cfa_offset */
 	.byte	0x80+8, 2		/* DW_CFA_offset %eip, 2*-4 */
@@ -1059,9 +1100,9 @@  L(EFDE6):
 	.set	L(set7),L(EFDE7)-L(SFDE7)
 	.long	L(set7)			/* FDE Length */
 L(SFDE7):
-	.long	L(SFDE7)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE7, CIE)			/* FDE CIE offset */
 	.long	PCREL(L(UW27))		/* Initial location */
-	.long	L(UW31)-L(UW27)		/* Address range */
+	LEN(UW31, UW27)			/* Address range */
 	.byte	0			/* Augmentation size */
 	ADV(UW28, UW27)
 	.byte	0xe, closure_FS+4	/* DW_CFA_def_cfa_offset */
@@ -1073,14 +1114,13 @@  L(SFDE7):
 #endif
 	.balign	4
 L(EFDE7):
-
 #if !FFI_NO_RAW_API
 	.set	L(set8),L(EFDE8)-L(SFDE8)
 	.long	L(set8)			/* FDE Length */
 L(SFDE8):
-	.long	L(SFDE8)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE8, CIE)			/* FDE CIE offset */
 	.long	PCREL(L(UW32))		/* Initial location */
-	.long	L(UW40)-L(UW32)		/* Address range */
+	LEN(UW40, UW32)			/* Address range */
 	.byte	0			/* Augmentation size */
 	ADV(UW33, UW32)
 	.byte	0xe, raw_closure_S_FS+4	/* DW_CFA_def_cfa_offset */
@@ -1102,9 +1142,9 @@  L(EFDE8):
 	.set	L(set9),L(EFDE9)-L(SFDE9)
 	.long	L(set9)			/* FDE Length */
 L(SFDE9):
-	.long	L(SFDE9)-L(CIE)		/* FDE CIE offset */
+	LEN(SFDE9, CIE)			/* FDE CIE offset */
 	.long	PCREL(L(UW41))		/* Initial location */
-	.long	L(UW52)-L(UW41)		/* Address range */
+	LEN(UW52, UW41)			/* Address range */
 	.byte	0			/* Augmentation size */
 	ADV(UW42, UW41)
 	.byte	0xe, 0			/* DW_CFA_def_cfa_offset */
@@ -1141,8 +1181,12 @@  L(EFDE9):
 @feat.00 = 1
 #endif
 
-#ifdef __APPLE__
+#if defined(__APPLE__)
     .subsections_via_symbols
+# if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&		\
+   __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 1070 && __clang__
+/* compact unwind is not used with GCC at present, was not present before 10.6
+   but has some bugs there, so do not emit until 10.7.  */
     .section __LD,__compact_unwind,regular,debug
 
     /* compact unwind for ffi_call_i386 */
@@ -1216,6 +1260,7 @@  L(EFDE9):
     .long    0x04000000 /* use dwarf unwind info */
     .long    0
     .long    0
+#endif /* use compact unwind */
 #endif /* __APPLE__ */
 
 #endif /* ifndef _MSC_VER */