From 4dc3d8f8325994d737f1959c1554480f4ccbc60f Mon Sep 17 00:00:00 2001
From: Aryadev Chavali <aryadev@aryadevchavali.com>
Date: Fri, 30 May 2025 08:12:49 +0100
Subject: Fix issue with memory allocations in lisp::serialise

Was to do with sv_make.
---
 lib/sv.c    |  3 ++-
 lisp/lisp.c |  8 +++++++-
 oats.org    | 24 +++++++++++++++---------
 3 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/lib/sv.c b/lib/sv.c
index b2425b8..a83f303 100644
--- a/lib/sv.c
+++ b/lib/sv.c
@@ -60,7 +60,8 @@ sv_t sv_chop(sv_t sv, u64 size)
 
 sv_t sv_concat(arena_t *allocator, sv_t a, sv_t b)
 {
-  sv_t c = sv_make(allocator, a.data, a.size + b.size);
+  sv_t c = sv_make(allocator, NULL, a.size + b.size);
+  memcpy(c.data, a.data, a.size);
   memcpy(c.data + a.size, b.data, b.size);
   return c;
 }
diff --git a/lisp/lisp.c b/lisp/lisp.c
index 24a4788..e1524a4 100644
--- a/lisp/lisp.c
+++ b/lisp/lisp.c
@@ -252,7 +252,13 @@ sv_t serialise(context_t *ctx, lisp_t *ptr)
         lmember = CAR(lmember);
 
       sv_t member = serialise(ctx, lmember);
-      s           = sv_concat(&ctx->scratch, s, member);
+      if (!s.data)
+        s = member;
+      else
+        s = sv_concat(&ctx->scratch, s, member);
+
+      // NOTE: eventually this separator we add per item should be mutable at
+      // runtime.
       if (IS_TAG(lsp, CONS) && !CDR(lsp))
         continue;
       else if (IS_TAG(CDR(lsp), CONS))
diff --git a/oats.org b/oats.org
index dbad845..b53b516 100644
--- a/oats.org
+++ b/oats.org
@@ -4,15 +4,6 @@
 #+FILETAGS: :oats:
 
 * Issues :issues:
-** TODO Fix issue with memcpy overlap when string concatenating
-[[file:lisp/lisp.c::// FIXME: Something is going wrong here!]]
-
-Ideas on what's going wrong:
-- String sizes seem off
-- Maybe something is wrong with arena allocator; we use
-  [[file:lib/sv.c::newsv.data = arena_realloc(allocator, sv.data,
-  sv.size, newsv.size);][arena_realloc]] which seems to be the root of
-  the memcpy-overlap
 * Features :features:
 ** WIP Reader :reader:
 We want something a bit generic: able to handle reading from some
@@ -205,3 +196,18 @@ more work than the lowest byte (to look at it we'll need to push that
 byte all the way down).  So we'll be going for a low byte strategy by
 shifting the pointer up by one byte.  This leaves us with the lowest
 byte to play with as we choose.
+** DONE Fix issue with memcpy overlap when string concatenating
+[[file:lisp/lisp.c::// FIXME: Something is going wrong here!]]
+
+Ideas on what's going wrong:
+- String sizes seem off
+- Maybe something is wrong with arena allocator; we use
+  [[file:lib/sv.c::newsv.data = arena_realloc(allocator, sv.data,
+  sv.size, newsv.size);][arena_realloc]] which seems to be the root of
+  the memcpy-overlap
+
+2025-05-30 08:11:24: Was an issue with ~sv_make~; if you pass a data
+pointer, it will try to copy the size you passed as bytes from the
+pointer.  In ~sv_concat~ we pass the overall new size of the string
+we're allocating and pass in the first argument to copy in the initial
+part of the data first.
-- 
cgit v1.2.3-13-gbd6f