rts/m32: Accept any address within 4GB of program text

Previously m32 would assume that the program image was located near the
start of the address space and therefore assume that it wanted pages
in the bottom 4GB of address space. Instead we now check whether they
are within 4GB of whereever the program is loaded.

This is necessary on Windows, which now tends to place the image in high
memory. The eventual goal is to use m32 to allocate memory for linker
sections on Windows.

1 files changed, 1 insertions, 56 deletions

diff --git a/rts/Linker.c b/rts/Linker.c
index 6c13213092..c79f184f23 100644
--- a/rts/Linker.c
+++ b/rts/Linker.c
@@ -171,62 +171,7 @@ Mutex linker_mutex;
 /* Generic wrapper function to try and Resolve and RunInit oc files */
 int ocTryLoad( ObjectCode* oc );
 
-/* Link objects into the lower 2Gb on x86_64 and AArch64.  GHC assumes the
- * small memory model on this architecture (see gcc docs,
- * -mcmodel=small).
- *
- * MAP_32BIT not available on OpenBSD/amd64
- */
-#if defined(MAP_32BIT) && (defined(x86_64_HOST_ARCH) || (defined(aarch64_TARGET_ARCH) || defined(aarch64_HOST_ARCH)))
-#define MAP_LOW_MEM
-#define TRY_MAP_32BIT MAP_32BIT
-#else
-#define TRY_MAP_32BIT 0
-#endif
-
-#if defined(aarch64_HOST_ARCH)
-// On AArch64 MAP_32BIT is not available but we are still bound by the small
-// memory model. Consequently we still try using the MAP_LOW_MEM allocation
-// strategy.
-#define MAP_LOW_MEM
-#endif
-
-/*
- * Note [MAP_LOW_MEM]
- * ~~~~~~~~~~~~~~~~~~
- * Due to the small memory model (see above), on x86_64 and AArch64 we have to
- * map all our non-PIC object files into the low 2Gb of the address space (why
- * 2Gb and not 4Gb?  Because all addresses must be reachable using a 32-bit
- * signed PC-relative offset). On x86_64 Linux we can do this using the
- * MAP_32BIT flag to mmap(), however on other OSs (e.g. *BSD, see #2063, and
- * also on Linux inside Xen, see #2512), we can't do this.  So on these
- * systems, we have to pick a base address in the low 2Gb of the address space
- * and try to allocate memory from there.
- *
- * The same holds for aarch64, where the default, even with PIC, model
- * is 4GB. The linker is free to emit AARCH64_ADR_PREL_PG_HI21
- * relocations.
- *
- * We pick a default address based on the OS, but also make this
- * configurable via an RTS flag (+RTS -xm)
- */
-
-#if (defined(aarch64_TARGET_ARCH) || defined(aarch64_HOST_ARCH))
-// Try to use stg_upd_frame_info as the base. We need to be within +-4GB of that
-// address, otherwise we violate the aarch64 memory model. Any object we load
-// can potentially reference any of the ones we bake into the binary (and list)
-// in RtsSymbols. Thus we'll need to be within +-4GB of those,
-// stg_upd_frame_info is a good candidate as it's referenced often.
-#define MMAP_32BIT_BASE_DEFAULT (void*)&stg_upd_frame_info;
-#elif defined(MAP_32BIT) || DEFAULT_LINKER_ALWAYS_PIC
-// Try to use MAP_32BIT
-#define MMAP_32BIT_BASE_DEFAULT 0
-#else
-// A guess: 1Gb.
-#define MMAP_32BIT_BASE_DEFAULT 0x40000000
-#endif
-
-static void *mmap_32bit_base = (void *)MMAP_32BIT_BASE_DEFAULT;
+static void *mmap_32bit_base = LINKER_LOAD_BASE;
 
 static void ghciRemoveSymbolTable(StrHashTable *table, const SymbolName* key,
     ObjectCode *owner)