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Allow writing extra VBR sectors from external preloader file

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This commit is contained in:
Aiken Harris
2025-10-08 22:15:49 +02:00
parent f69b0a4214
commit fc13836423
1 changed files with 121 additions and 28 deletions
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149
tools/diskimg.c
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@@ -244,6 +244,8 @@ int main(int argc, char **argv)
long FormatPartition = 0;
long DiskSizeBytes = 0;
long DiskSizeMB = 0;
long MergedSize = 0;
long PreloaderSize = 0;
long SectorsToWrite = 0;
long VbrExtraSector = -1;
long VbrFileSize = -1;
@@ -254,9 +256,12 @@ int main(int argc, char **argv)
char Zero[SECTOR_SIZE] = {0};
uint8_t Mbr[SECTOR_SIZE] = {0};
uint8_t ImageVbr[SECTOR_SIZE * 2] = {0};
uint8_t *FullVbr = NULL;
uint8_t *MergedData = NULL;
uint8_t *PreloaderData = NULL;
uint8_t *FullVbrData = NULL;
const char *FileName = NULL;
const char *MbrFile = NULL;
const char *PreloadFile = NULL;
const char *VbrFile = NULL;
const char *CopyDir = NULL;
@@ -294,6 +299,11 @@ int main(int argc, char **argv)
/* Output file */
FileName = argv[++Index];
}
else if(strcmp(argv[Index], "-p") == 0 && Index + 1 < argc)
{
/* Preloader file */
PreloadFile = argv[++Index];
}
else if(strcmp(argv[Index], "-s") == 0 && Index + 1 < argc)
{
/* Disk size */
@@ -316,7 +326,15 @@ int main(int argc, char **argv)
if(DiskSizeMB <= 0 || FileName == NULL)
{
/* Missing required arguments, print usage */
fprintf(stderr, "Usage: %s -o <output.img> -s <size_MB> [-b <sector>] [-c <dir>] [-f 16|32] [-m <mbr.img>] [-v <vbr.img>]\n", argv[0]);
fprintf(stderr, "Usage: %s -o <output.img> -s <size_MB> [-b <sector>] [-c <dir>] [-f 16|32] [-m <mbr.img>] [-p <preload.bin>] [-v <vbr.img>]\n", argv[0]);
return 1;
}
/* Validate preload usage */
if(PreloadFile && !VbrFile)
{
/* Preloader code specified without VBR */
fprintf(stderr, "Error: Option -p (PRELOADER code) requires -v (VBR code) to be specified as well.\n");
return 1;
}
@@ -485,7 +503,7 @@ int main(int argc, char **argv)
VbrFileSize = GetSectorFileSize(VbrFile);
if(VbrFileSize < 0)
{
/* The GetFileSize function already prints a perror message */
/* Unable to determine VBR file size */
perror("Could not get size of VBR file\n");
return 1;
}
@@ -494,27 +512,28 @@ int main(int argc, char **argv)
if(VbrFileSize % SECTOR_SIZE != 0)
{
/* Unable to determine VBR file size */
perror("Failed to determine VBR file size");
perror("VBR file size is not a multiple of sector size\n");
return 1;
}
/* Calculate number of VBR sectors */
VbrTotalSectors = VbrFileSize / SECTOR_SIZE;
/* Allocate memory for the entire VBR file */
FullVbr = malloc(VbrFileSize);
if(!FullVbr)
FullVbrData = malloc(VbrFileSize);
if(!FullVbrData)
{
/* Memory allocation failed */
perror("Failed to allocate memory for VBR file");
perror("Failed to allocate memory for VBR file\n");
return 1;
}
/* Read the entire VBR file into the buffer */
if(LoadSectors(VbrFile, FullVbr, VbrTotalSectors) != 0)
if(LoadSectors(VbrFile, FullVbrData, VbrTotalSectors) != 0)
{
/* Failed to load VBR from file */
perror("Failed to load VBR from file");
free(FullVbr);
perror("Failed to load VBR from file\n");
free(FullVbrData);
return 1;
}
@@ -523,8 +542,8 @@ int main(int argc, char **argv)
if(fread(ImageVbr, 1, SECTOR_SIZE, File) != SECTOR_SIZE)
{
/* Failed to read VBR from disk image */
perror("Failed to read BPB from disk image");
free(FullVbr);
perror("Failed to read BPB from disk image\n");
free(FullVbrData);
fclose(File);
return 1;
}
@@ -533,21 +552,21 @@ int main(int argc, char **argv)
if(FatFormat == 32)
{
/* For FAT32, BPB is larger (up to offset 89) */
memcpy(&FullVbr[3], &ImageVbr[3], 87);
memcpy(&FullVbrData[3], &ImageVbr[3], 87);
}
else
{
/* For FAT16, BPB is smaller (up to offset 61) */
memcpy(&FullVbr[3], &ImageVbr[3], 59);
memcpy(&FullVbrData[3], &ImageVbr[3], 59);
}
/* Write the first 512 bytes of the final, merged VBR to the start of the partition */
fseek(File, Partition.StartLBA * SECTOR_SIZE, SEEK_SET);
if(fwrite(FullVbr, 1, SECTOR_SIZE, File) != SECTOR_SIZE)
if(fwrite(FullVbrData, 1, SECTOR_SIZE, File) != SECTOR_SIZE)
{
/* Failed to write VBR to disk image */
perror("Failed to write VBR to disk image");
free(FullVbr);
perror("Failed to write VBR to disk image\n");
free(FullVbrData);
fclose(File);
return 1;
}
@@ -555,6 +574,72 @@ int main(int argc, char **argv)
/* Handle extra VBR data if it exists */
if(FatFormat == 32)
{
/* Check if a preloader file was provided */
if(PreloadFile)
{
/* Get the size of the preloader file */
PreloaderSize = GetSectorFileSize(PreloadFile);
if(PreloaderSize < 0)
{
/* Unable to determine preloader file size */
perror("Could not get size of preloader file.\n");
free(FullVbrData);
return 1;
}
/* Check if preloader size is multiple of 512 bytes */
if(PreloaderSize % SECTOR_SIZE != 0)
{
/* Preloader file size is not a multiple of 512 bytes */
perror("Preloader file size is not a multiple of sector size\n");
free(FullVbrData);
return 1;
}
/* Allocate buffer for preloader */
PreloaderData = malloc((size_t)PreloaderSize);
if(!PreloaderData)
{
/* Memory allocation failed */
perror("Failed to allocate memory for preloader");
free(FullVbrData);
return 1;
}
/* Load preloader data */
if(LoadSectors(PreloadFile, PreloaderData, PreloaderSize / SECTOR_SIZE) != 0)
{
/* Failed to load preloader data */
perror("Failed to load Preloader code from file\n");
free(FullVbrData);
return 1;
}
/* Allocate new buffer for the first 512 bytes of VBR and preloader */
MergedSize = SECTOR_SIZE + PreloaderSize;
MergedData = malloc(MergedSize);
if(!MergedData)
{
/* Memory allocation failed */
perror("Failed to allocate memory for Preloader file\n");
free(PreloaderData);
free(FullVbrData);
return 1;
}
/* Merge VBR and preloader data */
memcpy(MergedData, FullVbrData, SECTOR_SIZE);
memcpy(MergedData + SECTOR_SIZE, PreloaderData, PreloaderSize);
/* Free old buffers and replace with merged data */
free(FullVbrData);
free(PreloaderData);
FullVbrData = MergedData;
/* Update VBR sectors count */
VbrTotalSectors = (MergedSize + SECTOR_SIZE - 1) / SECTOR_SIZE;
}
/* Check if there is extra VBR data to write */
if(VbrTotalSectors > 1)
{
@@ -569,7 +654,7 @@ int main(int argc, char **argv)
/* Failed to find a safe sector */
fprintf(stderr, "Error: Could not automatically find a safe space in the FAT32 reserved region for %ld extra VBR sectors.\n",
sectors_to_write);
free(FullVbr);
free(FullVbrData);
return 1;
}
}
@@ -583,7 +668,7 @@ int main(int argc, char **argv)
{
/* The remaining space is not large enough to fit the extra VBR data */
fprintf(stderr, "Error: VBR file is too large. Writing to sector %ld would exceed the FAT32 reserved region (32 sectors).\n", VbrLastSector);
free(FullVbr);
free(FullVbrData);
return 1;
}
@@ -596,18 +681,18 @@ int main(int argc, char **argv)
/* We are about to overwrite a critical sector */
fprintf(stderr, "Error: Writing VBR extra data would overwrite critical sector %d (%s).\n",
Fat32ReservedMap[Index].SectorNumber, Fat32ReservedMap[Index].Description);
free(FullVbr);
free(FullVbrData);
return 1;
}
}
/* Write the rest of the VBR data */
fseek(File, (Partition.StartLBA + VbrExtraSector) * SECTOR_SIZE, SEEK_SET);
if(fwrite(FullVbr + SECTOR_SIZE, 1, SectorsToWrite * SECTOR_SIZE, File) != (size_t)(SectorsToWrite * SECTOR_SIZE))
if(fwrite(FullVbrData + SECTOR_SIZE, 1, SectorsToWrite * SECTOR_SIZE, File) != (size_t)(SectorsToWrite * SECTOR_SIZE))
{
/* Failed to write extra VBR data to disk image */
perror("Failed to write extra VBR data to disk image");
free(FullVbr);
free(FullVbrData);
fclose(File);
return 1;
}
@@ -616,17 +701,17 @@ int main(int argc, char **argv)
else /* FatFormat == 16 */
{
/* Check if there is extra VBR data to write */
if(VbrTotalSectors > 1)
if(VbrTotalSectors > 1 || PreloadFile)
{
/* FAT16 only supports a 1-sector VBR */
fprintf(stderr, "Error: VBR file is %ld sectors, but FAT16 only supports a 1-sector VBR.\n", VbrTotalSectors);
free(FullVbr);
fprintf(stderr, "Error: FAT16 does not support multi-sector VBR or preloader data.\n");
free(FullVbrData);
return 1;
}
}
/* Free allocated memory */
free(FullVbr);
free(FullVbrData);
}
/* Close file */
@@ -644,8 +729,16 @@ int main(int argc, char **argv)
/* Compose VBR info string */
if(VbrExtraSector != -1)
{
/* VBR with extra data */
snprintf(VbrInfo, sizeof(VbrInfo), ", VBR written (extra data at sector %ld)", VbrExtraSector);
if(PreloadFile)
{
/* Preloader written */
snprintf(VbrInfo, sizeof(VbrInfo), ", VBR written (preloader at sector %ld)", VbrExtraSector);
}
else
{
/* VBR with extra data */
snprintf(VbrInfo, sizeof(VbrInfo), ", VBR written (extra data at sector %ld)", VbrExtraSector);
}
}
else
{