Fix cut-off check for 1-byte jump offset

The size of a 1-byte jump is 2, so the offset to the end of a the
jump for a negative distance is `distance - 2`. Similarly, the size
of a 4-byte jump is 5 or 6, so the offset from the end of the 4-byte
jump is `distance - 5` or `distance - 6`.

Also, add an assert to make sure the offset really does fit in 1 byte.

1 files changed, 4 insertions, 2 deletions

diff --git a/main.c b/main.c
index 273ee7f..eb74bc8 100644
--- a/main.c
+++ b/main.c
@@ -1,3 +1,4 @@
+#include <assert.h>
 #include "minias.h"
 
 /* Parsed assembly */
@@ -504,7 +505,7 @@ assemblejmp(const Jmp *j)
         } else {
             distance = target->wco - cursection->hdr.sh_size;
         }
-        if ((distance - 1) >= -128 && (distance - 5) <= 127) {
+        if (distance - 2 >= INT8_MIN && distance - (j->cc ? 6 : 5) <= INT8_MAX) {
             jmpsize = 1;
         } else {
             jmpsize = 4;
@@ -922,7 +923,8 @@ resolvereloc(Relocation *reloc)
     case R_X86_64_PC8:
         rdata = &reloc->section->data[reloc->offset];
         value = sym->offset - reloc->offset + reloc->addend;
-        rdata[0] = ((uint8_t)value & 0xff);
+        assert(value >= INT8_MIN && value <= INT8_MAX);
+        rdata[0] = value;
         return 1;
     case R_X86_64_PC32:
         rdata = &reloc->section->data[reloc->offset];