-#include "../includes/ghcconfig.h"
-
module PositionIndependentCode (
cmmMakeDynamicReference,
needImportedSymbols,
dynamicLinkerLabelInfo, mkPicBaseLabel,
labelDynamic, externallyVisibleCLabel )
-#if powerpc_TARGET_ARCH && linux_TARGET_OS
+#if linux_TARGET_OS
import CLabel ( mkForeignLabel )
#endif
import MachInstrs
import NCGMonad ( NatM, getNewRegNat, getNewLabelNat )
-import CmdLineOpts ( opt_PIC )
+import CmdLineOpts ( opt_PIC, opt_Static )
import Pretty
import qualified Outputable
| opt_PIC && externallyVisibleCLabel lbl = AccessViaSymbolPtr
howToAccessLabel _ _ = AccessDirectly
-#elif linux_TARGET_OS && powerpc_TARGET_ARCH
--- PowerPC Linux
---
--- PowerPC Linux is just plain broken.
--- While it's theoretically possible to use GOT offsets larger
--- than 16 bit, the standard crt*.o files don't, which leads to
--- linker errors as soon as the GOT size exceeds 16 bit.
--- Also, the assembler doesn't support @gotoff labels.
--- In order to be able to use a larger GOT, we circumvent the
--- entire GOT mechanism and do it ourselves (this is what GCC does).
-
--- In this scheme, we need to do _all data references_ (even refs
--- to static data) via a SymbolPtr when we are generating PIC.
--- Luckily, the PLT works as expected, so we can simply access
--- dynamically linked code via the PLT.
-
-howToAccessLabel _ _ | not opt_PIC = AccessDirectly
-howToAccessLabel True lbl
- = if labelDynamic lbl then AccessViaStub
- else AccessDirectly
-howToAccessLabel False lbl
- = AccessViaSymbolPtr
+#elif linux_TARGET_OS && powerpc64_TARGET_ARCH
+-- ELF PPC64 (powerpc64-linux), AIX, MacOS 9, BeOS/PPC
+
+howToAccessLabel True lbl = AccessDirectly -- actually, .label instead of label
+howToAccessLabel _ lbl = AccessViaSymbolPtr
#elif linux_TARGET_OS
-- ELF (Linux)
--
+-- ELF tries to pretend to the main application code that dynamic linking does
+-- not exist. While this may sound convenient, it tends to mess things up in
+-- very bad ways, so we have to be careful when we generate code for the main
+-- program (-dynamic but no -fPIC).
+--
-- Indirect access is required for references to imported symbols
--- from position independent code.
--- It is always possible to access something indirectly,
--- even when it's not necessary.
-
--- For code, we can use a relative jump to a piece of
--- stub code instead (this allows lazy binding of imported symbols).
+-- from position independent code. It is also required from the main program
+-- when dynamic libraries containing Haskell code are used.
howToAccessLabel isJump lbl
- -- no PIC -> the dynamic linker does everything for us
- | not opt_PIC = AccessDirectly
- -- if it's not imported, we need no indirection
- -- ("foo" will end up being accessed as "foo@GOTOFF")
- | not (labelDynamic lbl) = AccessDirectly
+ -- no PIC -> the dynamic linker does everything for us;
+ -- if we don't dynamically link to Haskell code,
+ -- it actually manages to do so without messing thins up.
+ | not opt_PIC && opt_Static = AccessDirectly
+
#if !i386_TARGET_ARCH
-- for Intel, we temporarily disable the use of the
-- Procedure Linkage Table, because PLTs on intel require the
-- a jump through the PLT is made.
-- TODO: make the i386 NCG ensure this before jumping to a
-- CodeStub label, so we can remove this special case.
- | isJump = AccessViaStub
+
+ -- As long as we're in a shared library ourselves,
+ -- we can use the plt.
+ -- NOTE: We might want to disable this, because this
+ -- prevents -fPIC code from being linked statically.
+ | isJump && labelDynamic lbl && opt_PIC = AccessViaStub
+
+ -- TODO: it would be OK to access non-Haskell code via a stub
+-- | isJump && labelDynamic lbl && not isHaskellCode lbl = AccessViaStub
+
+ -- Using code stubs for jumps from the main program to an entry
+ -- label in a dynamic library is deadly; this will cause the dynamic
+ -- linker to replace all references (even data references) to that
+ -- label by references to the stub, so we won't find our info tables
+ -- any more.
#endif
- | otherwise = AccessViaSymbolPtr
+
+ -- A dynamic label needs to be accessed via a symbol pointer.
+ -- NOTE: It would be OK to jump to foreign code via a PLT stub.
+ | labelDynamic lbl = AccessViaSymbolPtr
+
+#if powerpc_TARGET_ARCH
+ -- For PowerPC32 -fPIC, we have to access even static data
+ -- via a symbol pointer (see below for an explanation why
+ -- PowerPC32 Linux is especially broken).
+ | opt_PIC && not isJump = AccessViaSymbolPtr
+#endif
+
+ | otherwise = AccessDirectly
#else
--
| otherwise = empty
-#elif powerpc_TARGET_ARCH && linux_TARGET_OS
-
--- For PowerPC linux, we don't do anything unless we're generating PIC.
-needImportedSymbols = opt_PIC
+#elif linux_TARGET_OS && !powerpc32_TARGET_ARCH
--- If we're generating PIC, we need to create our own "fake GOT".
+-- ELF / Linux
+--
+-- In theory, we don't need to generate any stubs or symbol pointers
+-- by hand for Linux.
+--
+-- Reality differs from this in two areas.
+--
+-- 1) If we just use a dynamically imported symbol directly in a read-only
+-- section of the main executable (as GCC does), ld generates R_*_COPY
+-- relocations, which are fundamentally incompatible with reversed info
+-- tables. Therefore, we need a table of imported addresses in a writable
+-- section.
+-- The "official" GOT mechanism (label@got) isn't intended to be used
+-- in position dependent code, so we have to create our own "fake GOT"
+-- when not opt_PCI && not opt_Static.
+--
+-- 2) PowerPC Linux is just plain broken.
+-- While it's theoretically possible to use GOT offsets larger
+-- than 16 bit, the standard crt*.o files don't, which leads to
+-- linker errors as soon as the GOT size exceeds 16 bit.
+-- Also, the assembler doesn't support @gotoff labels.
+-- In order to be able to use a larger GOT, we have to circumvent the
+-- entire GOT mechanism and do it ourselves (this is also what GCC does).
+
+
+-- When needImportedSymbols is defined,
+-- the NCG will keep track of all DynamicLinkerLabels it uses
+-- and output each of them using pprImportedSymbol.
+#if powerpc_TARGET_ARCH
+ -- PowerPC Linux: -fPIC or -dynamic
+needImportedSymbols = opt_PIC || not opt_Static
+#else
+ -- i386 (and others?): -dynamic but not -fPIC
+needImportedSymbols = not opt_Static && not opt_PIC
+#endif
+-- gotLabel
+-- The label used to refer to our "fake GOT" from
+-- position-independent code.
gotLabel = mkForeignLabel -- HACK: it's not really foreign
FSLIT(".LCTOC1") Nothing False
+-- pprGotDeclaration
+-- Output whatever needs to be output once per .s file.
-- The .LCTOC1 label is defined to point 32768 bytes into the table,
-- to make the most of the PPC's 16-bit displacements.
+-- Only needed for PIC.
-pprGotDeclaration = vcat [
+pprGotDeclaration
+ | not opt_PIC = Pretty.empty
+ | otherwise = vcat [
ptext SLIT(".section \".got2\",\"aw\""),
ptext SLIT(".LCTOC1 = .+32768")
]
-- We generate one .long literal for every symbol we import;
-- the dynamic linker will relocate those addresses.
-
+
pprImportedSymbol importedLbl
| Just (SymbolPtr, lbl) <- dynamicLinkerLabelInfo importedLbl
= vcat [
: ADD picReg picReg (RIReg tmp)
: insns)
return (CmmProc info lab params (b' : tail blocks) : gotOffset : statics)
-#else
-initializePicBase picReg proc = panic "initializePicBase"
+#elif i386_TARGET_ARCH && linux_TARGET_OS
--- TODO:
--- i386_TARGET_ARCH && linux_TARGET_OS:
--- generate something like:
+-- We cheat a bit here by defining a pseudo-instruction named FETCHGOT
+-- which pretty-prints as:
-- call 1f
-- 1: popl %picReg
-- addl __GLOBAL_OFFSET_TABLE__+.-1b, %picReg
--- It might be a good idea to use a FETCHPC pseudo-instruction (like for PowerPC)
--- in order to avoid having to create a new basic block.
--- ((FETCHPC reg) should pretty-print as call 1f; 1: popl reg)
+-- (See PprMach.lhs)
+
+initializePicBase picReg (CmmProc info lab params blocks : statics)
+ = return (CmmProc info lab params (b':tail blocks) : statics)
+ where BasicBlock bID insns = head blocks
+ b' = BasicBlock bID (FETCHGOT picReg : insns)
+
+#else
+initializePicBase picReg proc = panic "initializePicBase"
-- mingw32_TARGET_OS: not needed, won't be called
projects / ghc-hetmet.git / blobdiff