compiler/blob: make blob_reserve_bytes() more useful

Despite the name, it could only be used if you immediately wrote to the
pointer. Noboby was using it outside of one test, so clearly this
behavior wasn't that useful. Instead, make it return an offset into the
data buffer so that the result isn't invalidated if you later write to
the blob. In conjunction with blob_overwrite_bytes(), this will be
useful for leaving a placeholder and then filling it in later, which
we'll need to do for handling phi nodes when serializing NIR.

v2 (Jason Ekstrand):
 - Detect overflow in the offset + to_write computation

Reviewed-by: Nicolai Hähnle <[email protected]>
Reviewed-by: Jordan Justen <[email protected]>

1 files changed, 5 insertions, 5 deletions

diff --git a/src/compiler/blob.c b/src/compiler/blob.c
index f3ff5d6862e..65c450ee979 100644
--- a/src/compiler/blob.c
+++ b/src/compiler/blob.c
@@ -132,7 +132,7 @@ blob_overwrite_bytes(struct blob *blob,
                      size_t to_write)
 {
    /* Detect an attempt to overwrite data out of bounds. */
-   if (blob->size < offset + to_write)
+   if (offset + to_write < offset || blob->size < offset + to_write)
       return false;
 
    VG(VALGRIND_CHECK_MEM_IS_DEFINED(bytes, to_write));
@@ -158,15 +158,15 @@ blob_write_bytes(struct blob *blob, const void *bytes, size_t to_write)
    return true;
 }
 
-uint8_t *
+ssize_t
 blob_reserve_bytes(struct blob *blob, size_t to_write)
 {
-   uint8_t *ret;
+   ssize_t ret;
 
    if (! grow_to_fit (blob, to_write))
-      return NULL;
+      return -1;
 
-   ret = blob->data + blob->size;
+   ret = blob->size;
    blob->size += to_write;
 
    return ret;