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fix: stack overflow in turbo_init_rotation + TURBO_D static_assert #23

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Merged
TheTom merged 1 commit into from
Mar 31, 2026
Merged

fix: stack overflow in turbo_init_rotation + TURBO_D static_assert #23

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16 changes: 12 additions & 4 deletions ggml/src/ggml-turbo-quant.c
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,12 @@ int turbo3_cpu_wht_group_size = 0;
#define TURBO_D 128 /* rotation group size = head_dim (independent of block size) */
#define TURBO_QJL_CONST 1.2533141373155003f /* sqrt(pi/2) */

/* TURBO_D must match QK_TURBO3_GROUP from ggml-common.h — they represent
* the same rotation group size but are defined separately. Guard against
* silent divergence so GPU kernels and CPU reference stay in sync. */
static_assert(TURBO_D == QK_TURBO3_GROUP,
"TURBO_D must equal QK_TURBO3_GROUP (rotation group size)");

/* Optimal centroids from paper (scaled by 1/sqrt(d)) */
/* 1-bit: ±sqrt(2/(pi*d)) */
static const float CENTROIDS_1BIT[2] = { -0.070711f, 0.070711f }; /* for d=128 */
Expand Down Expand Up @@ -66,16 +72,18 @@ static void turbo_init_rotation(void) {

const int d = TURBO_D;

/* Generate random Gaussian matrix */
/* Generate random Gaussian matrix directly into turbo_rotation.
* Previous code used a 64KB stack-local G[128*128] then memcpy'd —
* this segfaults on llama.cpp worker threads with reduced stack
* sizes (512KB macOS, 64KB some Linux configs). Writing directly
* into the static array avoids the stack allocation entirely. */
turbo_prng_seed(TURBO_SEED_ROTATION);
float G[TURBO_D * TURBO_D];
for (int i = 0; i < d * d; i++) {
G[i] = (float)turbo_prng_normal();
turbo_rotation[i] = (float)turbo_prng_normal();
}

/* QR decomposition via modified Gram-Schmidt */
/* Q stored column-major in turbo_rotation */
memcpy(turbo_rotation, G, d * d * sizeof(float));

for (int j = 0; j < d; j++) {
/* Normalize column j */
Expand Down
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