Getting "Serious error when reading debug info" when using mmap

Hi,
I'm getting a strange error when running Valgrind.

--23266-- WARNING: Serious error when reading debug info
--23266-- When reading debug info from /tmp/db/test.txt:
--23266-- can't read file to inspect ELF header

Note that the file in question is a data file, which I'm mmaping

I can reproduce this using the following code:
https://gist.github.com/ayende/d65a7a3c06556d62c8fa0f88b04ea449

valgrind-3.16.1 & clang version 10.0.0-4ubuntu1

This seems to be related to mmaping a file, but I can't figure out exactly
why

Running Valgrind under `strace` gives:

    mmap(0x4e4d000, 65536, PROT_READ, MAP_SHARED|MAP_FIXED, 3, 0) =
0x4e4d000
    statx(3, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL,
{stx_mask=STATX_ALL, stx_attributes=0, stx_mode=S_IFREG|0600,
stx_size=262144, ...}) = 0
    readlink("/proc/self/fd/3", "/tmp/db/test.txt", 4096) = 16
    statx(AT_FDCWD, "/tmp/db/test.txt", AT_STATX_SYNC_AS_STAT, STATX_ALL,
{stx_mask=STATX_ALL, stx_attributes=0, stx_mode=S_IFREG|0600,
stx_size=262144, ...}) = 0
    pread64(3, 0x10032c68a0, 1024, 0)       = -1 EINVAL (Invalid argument)
    getpid()                                = 23260
    write(1027, "--23260-- WARNING: Serious error"..., 57--23260-- WARNING:
Serious error when reading debug info
    ) = 57
    getpid()                                = 23260
    write(1027, "--23260-- When reading debug inf"..., 57--23260-- When
reading debug info from /tmp/db/test.txt:

So it looks like the `pread64()` code is failing, but I can't figure out
why that is the case, or why it would cause Valgrind to give this error.
Any ideas?

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