luke
/
icestorm
mirror of https://github.com/YosysHQ/icestorm.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

icepack: Fix Windows-only stack overflow in CRAM pbm generation (fixes #241) 

On Windows, attempting to generate a netpbm image of the CRAM with
`icepack -b` causes the tool to crash after writing only the netpbm
header due to a stack overflow. The bug did not appear on Linux.

This was traced to a large stack-allocated variable length array
(`tile_type`) inside `FpgaConfig::write_cram_pbm`. For an 8k ice40 with
4 banks, `cram_width = 872` and `cram_height = 272` the `tile_type`
array ends up at `4 * 872 * 272 * sizeof(uint32_t) =` 3794944 bytes, or
about 3.6 MiB.

The fix replaces the large stack VLA with an array of 4 (bank) 2D C++
vectors, moving the large amount of data to the heap. Even though the
fix is not in a Windows-specific code path (and hence applies to all
platforms), I think it's wise to eliminate such a large stack allocation
entirely.

The fix has been tested working on both Windows and an Ubuntu WSL
install.
This commit is contained in:
The6P4C 2019-12-08 23:27:46 +10:00
parent 0ec00d892a
commit 578037dedf
1 changed files with 19 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
icepack/icepack.cc
View File

@ -968,7 +968,25 @@ void FpgaConfig::write_cram_pbm(std::ostream &ofs, int bank_num) const
ofs << "P3\n";
ofs << stringf("%d %d\n", 2*this->cram_width, 2*this->cram_height);
ofs << "255\n";
uint32_t tile_type[4][this->cram_width][this->cram_height];
vector<vector<uint32_t>> tile_type[4];
// We require random access to tile_type, so ensure that each column of each
// bank is initialised so that all possible indices are valid
for (int bank = 0; bank < 4; bank++) {
tile_type[bank].reserve(this->cram_width);
for (int x = 0; x < this->cram_width; x++) {
tile_type[bank].push_back(vector<uint32_t>(this->cram_height));
for (int y = 0; y < this->cram_height; y++) {
// Initialisation value unimportant - will be overwritten during
// image generation
tile_type[bank][x].push_back(0);
}
}
}
for (int y = 0; y <= this->chip_height()+1; y++)
for (int x = 0; x <= this->chip_width()+1; x++)
{