`espflash save-image` produces a different image inside and outside of Nix package build

[flippette]

I'm building a firmware with this flake, and espflash is being called like this:

postInstall = ''
  # generate a flat firmware binary (for OTA, etc.)
  ${espflash}/bin/espflash save-image \
    --chip esp32c6 \
    $out/bin/$pname \
    $out/bin/$pname-$version.bin
'';

Running esptool on this generated firmware binary shows that the checksum and validation hash are invalid:

esp-template on  main ❯ nix run nixpkgs#esptool -- image_info result/bin/esp-template-0.1.0.bin | tail -n 2
Checksum: 42 (invalid - calculated 52)
Validation Hash: 7ee766842072a8493801cbfd70096c5541a57c15ff2d8add597f54793bf0847f (invalid)

However, if I run espflash save-image myself after the build on the same ELF binary, that image is valid by esptool:

esp-template on  main ❯ espflash save-image --chip esp32c6 result/bin/esp-template output.bin
Chip type:         esp32c6
Merge:             false
Skip padding:      false
App/part. size:    28,160/4,128,768 bytes, 0.68%
[2025-07-30T19:42:31Z INFO ] Image successfully saved!
esp-template on  main [?] ❯ nix run nixpkgs#esptool -- image_info output.bin | tail -n 2
Checksum: 52 (valid)
Validation Hash: 940606d072d9b290e9f0af23fbba19a11f537d0f73a12c72d538a563e9a1aaed (valid)

Diffing the 2 binary files shows this:

esp-template on  main [?] ❯ diff valid.hex invalid.hex
1758,1760c1758,1760
< 00006dd0: 0000 0000 0000 0000 0000 0000 0000 0052  ...............R
< 00006de0: 9406 06d0 72d9 b290 e9f0 af23 fbba 19a1  ....r......#....
< 00006df0: 1f53 7d0f 73a1 2c72 d538 a563 e9a1 aaed  .S}.s.,r.8.c....
---
> 00006dd0: 0000 0000 0000 0000 0000 0000 0000 0042  ...............B
> 00006de0: 4bdc b57b 2dbb 21cc 913a 311a e3e5 03a7  K..{-.!..:1.....
> 00006df0: f325 8ec7 f04b 3257 ce4e 45b2 4075 48ca  .%...K2W.NE.@uH.

espflash is version 4.0.1 both inside and outside of the flake.

[SergioGasquez]

Hi! I dont use Nix, so here are a few questions:

• How are you building the application?

I run espflash save-image myself after the build on the same ELF binary

• Are you building the binary outside the flake or you run both espflash commands to the ELF generated inside the flake?
• What is the output of the espflash command inside the flake? Maybe it would be worth to enable debug logs and see the output

[flippette]

Hi!

How are you building the application?

The flake just runs cargo build --release on the source code, and then espflash as seen in the above snippet.

Are you building the binary outside the flake or do you run both espflash commands to the ELF generated inside the flake?

I run both espflash commands on the same ELF generated inside the flake, yes.

What is the output of the espflash command inside the flake?

Here's espflash inside the flake (with RUST_LOG=debug):

esp-template> [2025-08-05T13:28:43Z DEBUG] SaveImage(
esp-template>         SaveImageArgs {
esp-template>             image: "/nix/store/x3aba45v2nnf89yfbygn49r4nys64arr-esp-template-0.1.0/bin/esp-template",
esp-template>             flash_config_args: FlashConfigArgs {
esp-template>                 flash_freq: None,
esp-template>                 flash_mode: None,
esp-template>                 flash_size: None,
esp-template>             },
esp-template>             save_image_args: SaveImageArgs {
esp-template>                 chip: Esp32c6,
esp-template>                 file: "/nix/store/x3aba45v2nnf89yfbygn49r4nys64arr-esp-template-0.1.0/bin/esp-template-0.1.0.bin",
esp-template>                 merge: false,
esp-template>                 skip_padding: false,
esp-template>                 xtal_freq: None,
esp-template>                 image: ImageArgs {
esp-template>                     min_chip_rev: 0,
esp-template>                     mmu_page_size: None,
esp-template>                     check_app_descriptor: true,
esp-template>                 },
esp-template>             },
esp-template>             format: EspIdf,
esp-template>             idf_format_args: IdfFormatArgs {
esp-template>                 bootloader: None,
esp-template>                 partition_table: None,
esp-template>                 partition_table_offset: None,
esp-template>                 target_app_partition: None,
esp-template>             },
esp-template>         },
esp-template>     ), false
esp-template> [2025-08-05T13:28:43Z DEBUG] Config: ProjectConfig {
esp-template>         baudrate: None,
esp-template>         format: EspIdf,
esp-template>         idf_format_args: IdfFormatArgs {
esp-template>             bootloader: None,
esp-template>             partition_table: None,
esp-template>             partition_table_offset: None,
esp-template>             target_app_partition: None,
esp-template>         },
esp-template>         flash: FlashSettings {
esp-template>             mode: None,
esp-template>             size: None,
esp-template>             freq: None,
esp-template>         },
esp-template>     }
esp-template> [2025-08-05T13:28:43Z DEBUG] Port Config: PortConfig {
esp-template>         connection: Connection {
esp-template>             serial: None,
esp-template>         },
esp-template>         usb_device: [],
esp-template>         save_path: "/homeless-shelter/.config/espflash/espflash_ports.toml",
esp-template>     }
esp-template> Chip type:         esp32c6
esp-template> Merge:             false
esp-template> Skip padding:      false
esp-template> [2025-08-05T13:28:43Z DEBUG] Updating bootloader SHA256 from 98f67077a1bf734816177da0fb3a022f79f2213c856f88950ae7c23e03c282d0 to 9f29d1b6842faa42b969c930a0c42ced911d61f91123648f7134a4e93c8bb117
esp-template> App/part. size:    28,160/4,128,768 bytes, 0.68%
esp-template> [2025-08-05T13:28:43Z INFO ] Image successfully saved!

And here's espflash outside the flake, run on the same ELF (also with RUST_LOG=debug):

[2025-08-05T13:30:30Z DEBUG] SaveImage(
        SaveImageArgs {
            image: "result/bin/esp-template",
            flash_config_args: FlashConfigArgs {
                flash_freq: None,
                flash_mode: None,
                flash_size: None,
            },
            save_image_args: SaveImageArgs {
                chip: Esp32c6,
                file: "fw.bin",
                merge: false,
                skip_padding: false,
                xtal_freq: None,
                image: ImageArgs {
                    min_chip_rev: 0,
                    mmu_page_size: None,
                    check_app_descriptor: true,
                },
            },
            format: EspIdf,
            idf_format_args: IdfFormatArgs {
                bootloader: None,
                partition_table: None,
                partition_table_offset: None,
                target_app_partition: None,
            },
        },
    ), false
[2025-08-05T13:30:30Z DEBUG] Call<Prepare>
[2025-08-05T13:30:30Z DEBUG] GET https://crates.io/******
[2025-08-05T13:30:30Z DEBUG] Resolved: ArrayVec { len: 12, arr: [[2600:9000:26b8:4c00:c:7ed3:240:93a1]:443, [2600:9000:26b8:fc00:c:7ed3:240:93a1]:443, [2600:9000:26b8:9a00:c:7ed3:240:93a1]:443, [2600:9000:26b8:1e00:c:7ed3:240:93a1]:443, [2600:9000:26b8:8e00:c:7ed3:240:93a1]:443, [2600:9000:26b8:1c00:c:7ed3:240:93a1]:443, [2600:9000:26b8:9200:c:7ed3:240:93a1]:443, [2600:9000:26b8:c000:c:7ed3:240:93a1]:443, 108.157.254.108:443, 108.157.254.74:443, 108.157.254.55:443, 108.157.254.119:443] }
[2025-08-05T13:30:30Z DEBUG] Connected TcpStream to [2600:9000:26b8:4c00:c:7ed3:240:93a1]:443
[2025-08-05T13:30:30Z DEBUG] No cached session for DnsName("crates.io")
[2025-08-05T13:30:30Z DEBUG] Not resuming any session
[2025-08-05T13:30:30Z DEBUG] Wrapped TLS
[2025-08-05T13:30:30Z DEBUG] Call<SendRequest>
[2025-08-05T13:30:30Z DEBUG] Request { method: GET, uri: https://crates.io/******, version: HTTP/1.1, headers: {"accept-encoding": "gzip", "user-agent": "ureq/3.0.12", "accept": "*/*", "host": "crates.io"} }
[2025-08-05T13:30:30Z DEBUG] Using ciphersuite TLS13_AES_128_GCM_SHA256
[2025-08-05T13:30:30Z DEBUG] Not resuming
[2025-08-05T13:30:30Z DEBUG] TLS1.3 encrypted extensions: ServerExtensions { server_name_ack: (), unknown_extensions: {}, .. }
[2025-08-05T13:30:30Z DEBUG] ALPN protocol is None
[2025-08-05T13:30:30Z DEBUG] Call<RecvResponse>
[2025-08-05T13:30:31Z DEBUG] Call<RecvBody>
[2025-08-05T13:30:31Z DEBUG] Response { status: 200, version: HTTP/1.1, headers: {"content-type": "application/json", "transfer-encoding": "chunked", "connection": "keep-alive", "content-encoding": "gzip", "date": "Tue, 05 Aug 2025 13:30:31 GMT", "server": "Heroku", "<NOTICE>": "14 HEADERS ARE REDACTED"} }
[2025-08-05T13:30:31Z DEBUG] Decoding gzip
[2025-08-05T13:30:31Z DEBUG] Call<Cleanup>
[2025-08-05T13:30:31Z DEBUG] Return to pool: PoolKey { scheme: "https", authority: crates.io, proxy: None }
[2025-08-05T13:30:31Z DEBUG] Config: ProjectConfig {
        baudrate: None,
        format: EspIdf,
        idf_format_args: IdfFormatArgs {
            bootloader: None,
            partition_table: None,
            partition_table_offset: None,
            target_app_partition: None,
        },
        flash: FlashSettings {
            mode: None,
            size: None,
            freq: None,
        },
    }
[2025-08-05T13:30:31Z DEBUG] Port Config: PortConfig {
        connection: Connection {
            serial: None,
        },
        usb_device: [],
        save_path: "/home/flippette/.config/espflash/espflash_ports.toml",
    }
Chip type:         esp32c6
Merge:             false
Skip padding:      false
[2025-08-05T13:30:31Z DEBUG] Updating bootloader SHA256 from 98f67077a1bf734816177da0fb3a022f79f2213c856f88950ae7c23e03c282d0 to 9f29d1b6842faa42b969c930a0c42ced911d61f91123648f7134a4e93c8bb117
App/part. size:    28,160/4,128,768 bytes, 0.68%
[2025-08-05T13:30:31Z INFO ] Image successfully saved!