Native Inference: Testing an SLM (L3.1-8B-I) on C Pointer Logic

Source: Dev.to

Setup

I recently installed llama-cli on my Linux Debian laptop and ran it using native inference—executing the llama-cli binaries directly with Linux commands and flags. By compiling from source I could target specific CPU flags (e.g., AVX‑512) to get the most out of my hardware.

For this test I used the following model:

• Llama 3.1 8B Instruct (Q4_K_M GGUF) – referred to as Llama‑3.1 throughout the article.

The goal was to see how the model handles a simple C program that contains pointer logic.

C Program

#include 
#include 
#include 

int main() {
    char *buffer = malloc(100 * sizeof(char));

    if (buffer == NULL) {
        return 1;
    }

    strcpy(buffer, "Llama 3.1 is running close to the metal.");
    printf("Buffer content: %s\n", buffer);

    // Intentional bug: No free(buffer) here.
    return 0;
}

Prompt given to the model

Explain the memory allocation here step‑by‑step.

Llama‑3.1’s Response

Here’s a step-by-step explanation of the memory allocation in the code:

char *buffer = malloc(100 * sizeof(char));

• malloc dynamically allocates a block of memory of the requested size.
• 100 * sizeof(char) equals 100 bytes because sizeof(char) is 1.
• The allocated block is stored in the pointer buffer.
• malloc returns NULL on failure.

if (buffer == NULL) { … }

• Checks whether the allocation succeeded.
• If buffer is NULL, the program exits with error code 1.

strcpy(buffer, "Llama 3.1 is running close to the metal.");

• Copies the string into the allocated memory.
• The allocated block is 100 bytes, so the copy succeeds, leaving the remaining bytes uninitialized.

free(buffer);

• Deallocates the memory allocated by malloc.
• This step is necessary to avoid a memory leak.

Note: In a real program you would typically check the return value of malloc and free the memory when it is no longer needed.

Analysis of the Model’s Output

The Hallucination

The original source code does not contain a free(buffer); call. Llama‑3.1 incorrectly added this line, a classic example of a model “hallucinating” a common best practice.

Accuracy

• Correctly described malloc and the null‑pointer check.
• Misidentified the presence of free(buffer);.

Math Check

The model claimed that 86 bytes remain after copying the string.
The actual string "Llama 3.1 is running close to the metal." is 39 characters long; with the terminating null byte it occupies 40 bytes.
Thus the remaining space is 100 – 40 = 60 bytes, not 86.

Takeaways

• Human verification is essential. Even a well‑behaved 8 B model can insert plausible but incorrect code.
• Prompt engineering matters. Precise prompts help guide the model, but they cannot eliminate hallucinations.
• Hardware‑side success. Running an 8 B model with AVX‑512 (or AVX‑2 on older hardware) demonstrates that useful inference can be performed without a GPU, making on‑device AI more accessible.

Ben Santora – January 2026