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Issue #430 - Ensure collection of vector fill

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Prevent an edge case where the stack object used to fill a large vector is not promoted to the heap.
This commit is contained in:
Justin Ethier 2020-12-24 13:50:00 -05:00
parent b218aacf65
commit 50cc213437
2 changed files with 14 additions and 6 deletions
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1
CHANGELOG.md
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@ -7,6 +7,7 @@ TODO: shared object functions no longe required since 0.14, update docs to refle
Bug Fixes
- When allocating large vectors the object used to fill such a vector may not be transported to the heap. This was a nasty bug that could lead to memory corruption.
- Sean Lynch fixed a bug where record type predicates do not check the length of the target before checking if the vector is actually a record.
- Do not attempt to call `eval` from the runtime if `(scheme eval)` has not been imported. Instead we now raise a Scheme error in this case instead of allowing the runtime to raise a C segmentation violation.

19
runtime.c
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@ -618,9 +618,16 @@ void add_mutation(void *data, object var, int index, object value)
// No need to track for minor GC purposes unless we are mutating
// a heap variable to point to a stack var.
//
// If var is on stack we'll get it anyway in minor GC,
// and if value is on heap we don't care (no chance of heap pointing to nursery)
if (!gc_is_stack_obj(&tmp, data, var) && gc_is_stack_obj(&tmp, data, value)) {
// If var is on stack we'll get it anyway in minor GC, and if value
// is on heap we don't care (no chance of heap pointing to nursery)
//
// There is one special case. For large vectors we use stack objects
// as a container to store "real" stack values that must be moved
// by the collector. In this case we pass -2 to force collection of
// these objects regardless of whether var is on the heap.
if ( (!gc_is_stack_obj(&tmp, data, var) &&
gc_is_stack_obj(&tmp, data, value)) ||
index == -2) {
thd->mutations = vpbuffer_add(thd->mutations,
&(thd->mutation_buflen),
thd->mutation_count,
@ -3059,10 +3066,10 @@ object Cyc_make_vector(void *data, object cont, int argc, object len, ...)
// Use write barrier to ensure fill is moved to heap if it is on the stack
// Otherwise if next minor GC misses fill it could be catastrophic
car(&tmp_pair) = fill;
add_mutation(data, &tmp_pair, -1, fill);
add_mutation(data, &tmp_pair, -2, fill);
// Add a special object to indicate full vector must be scanned by GC
opaque_ptr(&opq) = v;
add_mutation(data, &opq, -1, v);
add_mutation(data, &opq, -2, v);
} else {
v = alloca(sizeof(vector_type));
((vector) v)->hdr.mark = gc_color_red;
@ -3467,7 +3474,7 @@ object Cyc_list2vector(void *data, object cont, object l)
//add_mutation(data, &tmp_pair, -1, fill);
// Add a special object to indicate full vector must be scanned by GC
opaque_ptr(&opq) = v;
add_mutation(data, &opq, -1, v);
add_mutation(data, &opq, -2, v);
} else {
v = alloca(sizeof(vector_type));
((vector) v)->hdr.mark = gc_color_red;