linker: Add support for gdb's JIT interface

(cherry picked from commit 3b909208273c75fb3fe6b05b75c4fe9bf635ed68)

2 files changed, 119 insertions, 0 deletions

diff --git a/rts/linker/BufferBuilder.c b/rts/linker/BufferBuilder.c
new file mode 100644
index 0000000000..2c4f84836e
--- /dev/null
+++ b/rts/linker/BufferBuilder.c
@@ -0,0 +1,76 @@
+#include "Rts.h"
+
+struct BufferBuilder {
+    uint8_t *buffer; // start of buffer
+    uint8_t *head;   // next unfilled byte
+    uint8_t *end     // end of buffer
+};
+
+struct BufferBuilder buffer_builder_new(size_t initial_sz)
+{
+    uint8_t *buffer = stgMallocBytes(initial_sz, "new_buffer_builder");
+    return struct BufferBuilder {
+        .buffer = buffer,
+        .head = buffer,
+        .end = buffer + initial_sz,
+    };
+}
+
+void buffer_builder_free(struct BufferBuilder *bb)
+{
+    stgFree(bb->buffer);
+    bb->buffer = NULL;
+    bb->head = NULL;
+    bb->end = NULL;
+}
+
+size_t buffer_builder_filled_size(struct BufferBuilder *bb)
+{
+    return bb->head - bb->buffer;
+}
+
+size_t buffer_builder_reserved_size(struct BufferBuilder *bb)
+{
+    return bb->end - bb->buffer;
+}
+
+void buffer_builder_realloc(struct BufferBuilder *bb, size_t new_sz)
+{
+    size_t filled_sz = buffer_builder_filled_size(bb);
+    ASSERT(filled_sz <= new_sz);
+    uint8_t *buffer = stgReallocBytes(bb->buffer, new_sz, "new_buffer_builder");
+    bb->buffer = buffer;
+    bb->head = buffer + filled_sz;
+    bb->end = buffer + new_sz;
+}
+
+uint8_t *buffer_builder_push(struct BufferBuilder *bb, uint8_t *x, size_t sz)
+{
+    if (bb->head + sz > bb->end) {
+        buffer_builder_realloc(bb, 2*buffer_builder_reserved_size(bb));
+    }
+
+    memcpy(bb->head, x, sz);
+    uint8_t *ret = bb->head;
+    bb->head += sz;
+    return ret;
+}
+
+void buffer_builder_append(struct BufferBuilder *bb, struct BufferBuilder *src)
+{
+    size_t sz = buffer_builder_filled_size(src);
+    buffer_builder_push(bb, bb->buffer, sz);
+}
+
+#define DEFINE_BUILDER(ty) \
+    void buffer_builder_#ty(struct BufferBuilder *bb, ty#_t x) \
+        { return (ty#_t *) buffer_builder_push(bb, &x, sizeof(x)); }
+DEFINE_BUILDER(uint8)
+DEFINE_BUILDER(uint16)
+DEFINE_BUILDER(uint32)
+DEFINE_BUILDER(uint64)
+DEFINE_BUILDER(int8)
+DEFINE_BUILDER(int16)
+DEFINE_BUILDER(int32)
+DEFINE_BUILDER(int64)
+#undef DEFINE_BUILDER
diff --git a/rts/linker/JitObject.c b/rts/linker/JitObject.c
new file mode 100644
index 0000000000..bd8b432f9e
--- /dev/null
+++ b/rts/linker/JitObject.c
@@ -0,0 +1,43 @@
+#include "BufferBuilder.h"
+
+void *build_jit_object_coff(ObjectCode *oc)
+{
+    struct BufferBuilder bb = buffer_builder_new(4096);
+
+    // COFF header
+    buffer_builder_uint16(bb, IMAGE_FILE_MACHINE_AMD64);
+    buffer_builder_uint16(bb, 1); // NumberOfSections
+    buffer_builder_uint32(bb, 0); // TimeDateStamp
+    uint32_t *ptr_to_symbol_table = buffer_builder_uint32(bb, 0); // PointerToSymbolTable
+    buffer_builder_uint32(bb, n_syms); // NumberOfSymbols
+    buffer_builder_uint16(bb, 0); // SizeOfOptionalHeader
+    buffer_builder_uint16(bb, 0); // Characteristics
+
+    // Sections
+    buffer_builder_push(bb, ".text\0\0\0", 8); // Name
+    buffer_builder_uint32(bb, sect_sz);        // VirtualSize
+    buffer_builder_uint32(bb, sect_base);      // VirtualAddress
+    buffer_builder_uint32(bb, 0);              // SizeOfRawData
+    buffer_builder_uint32(bb, 0);              // PointerToRawData
+    buffer_builder_uint32(bb, 0);              // PointerToRelocations
+    buffer_builder_uint32(bb, 0);              // PointerToLinenumbers
+    buffer_builder_uint16(bb, 0);              // NumberOfRelocations
+    buffer_builder_uint16(bb, 0);              // NumberOfLinenumbers
+    buffer_builder_uint32(bb, 0);              // Characteristics
+
+    struct BufferBuilder strings = buffer_builder_new(4096);
+    for (int i=0; i < oc->n_symbols; i++) {
+        Symbol_t *sym = oc->symbols[i];
+        size_t offset = buffer_builder_filled_size(strings);
+        buffer_builder_push(strings, sym->name);
+        buffer_builder_uint32(bb, 0);
+        buffer_builder_uint32(bb, offset); // RawName index
+        buffer_builder_uint32(bb, value);  // Value
+        buffer_builder_uint16(bb, 1);      // SectionNumber
+        buffer_builder_uint8(bb, 0x20);    // StorageClass
+        buffer_builder_uint8(bb, 0);       // NumberOfAuxSymbols
+    }
+
+    buffer_builder_append(bb, strings);
+    return bb->start;
+}