When building with Clang we encounter this warning:
| drivers/net/wireless/mediatek/mt7601u/debugfs.c:92:6: error: format
| specifies type 'unsigned char' but the argument has type 'int'
| [-Werror,-Wformat] dev->ee->reg.start + dev->ee->reg.num - 1);
The format specifier used is `%hhu` which describes a u8. Both
`dev->ee->reg.start` and `.num` are u8 as well. However, the expression
as a whole is promoted to an int as you cannot get smaller-than-int from
addition. Therefore, to fix the warning, use the promoted-to-type's
format specifier -- in this case `%d`.
example:
```
uint8_t a = 4, b = 7;
int size = sizeof(a + b - 1);
printf("%d\n", size);
// output: 4
```
See more:
(https://wiki.sei.cmu.edu/confluence/display/c/INT02-C.+Understand+integer+conversion+rules)
"Integer types smaller than int are promoted when an operation is
performed on them. If all values of the original type can be represented
as an int, the value of the smaller type is converted to an int;
otherwise, it is converted to an unsigned int."
Signed-off-by: Justin Stitt <[email protected]>
---
Note: This patch silences the -Wformat warning for this file (which is
the goal) but in reality all instances of `%hh[dux]` should be converted
to `%[dux]` for this file and probably every file. That's a bit larger
scope than the goal of enabling -Wformat for Clang builds, though.
drivers/net/wireless/mediatek/mt7601u/debugfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/wireless/mediatek/mt7601u/debugfs.c b/drivers/net/wireless/mediatek/mt7601u/debugfs.c
index 20669eacb66e..230b0e1061a7 100644
--- a/drivers/net/wireless/mediatek/mt7601u/debugfs.c
+++ b/drivers/net/wireless/mediatek/mt7601u/debugfs.c
@@ -88,7 +88,7 @@ mt7601u_eeprom_param_show(struct seq_file *file, void *data)
dev->ee->rssi_offset[0], dev->ee->rssi_offset[1]);
seq_printf(file, "Reference temp: %hhx\n", dev->ee->ref_temp);
seq_printf(file, "LNA gain: %hhx\n", dev->ee->lna_gain);
- seq_printf(file, "Reg channels: %hhu-%hhu\n", dev->ee->reg.start,
+ seq_printf(file, "Reg channels: %hhu-%d\n", dev->ee->reg.start,
dev->ee->reg.start + dev->ee->reg.num - 1);
seq_puts(file, "Per rate power:\n");
--
2.37.0.144.g8ac04bfd2-goog
On Mon, 11 Jul 2022 14:29:32 -0700 Justin Stitt wrote:
> When building with Clang we encounter this warning:
> | drivers/net/wireless/mediatek/mt7601u/debugfs.c:92:6: error: format
> | specifies type 'unsigned char' but the argument has type 'int'
> | [-Werror,-Wformat] dev->ee->reg.start + dev->ee->reg.num - 1);
>
> The format specifier used is `%hhu` which describes a u8. Both
> `dev->ee->reg.start` and `.num` are u8 as well. However, the expression
> as a whole is promoted to an int as you cannot get smaller-than-int from
> addition. Therefore, to fix the warning, use the promoted-to-type's
> format specifier -- in this case `%d`.
Acked-by: Jakub Kicinski <[email protected]>
On Mon, 2022-07-11 at 14:29 -0700, Justin Stitt wrote:
> When building with Clang we encounter this warning:
> > drivers/net/wireless/mediatek/mt7601u/debugfs.c:92:6: error: format
> > specifies type 'unsigned char' but the argument has type 'int'
> > [-Werror,-Wformat] dev->ee->reg.start + dev->ee->reg.num - 1);
>
> The format specifier used is `%hhu` which describes a u8. Both
> `dev->ee->reg.start` and `.num` are u8 as well. However, the expression
> as a whole is promoted to an int as you cannot get smaller-than-int from
> addition. Therefore, to fix the warning, use the promoted-to-type's
> format specifier -- in this case `%d`.
I think whenever a sizeof(unsigned type) that is less than sizeof(int) is
emitted with vsprintf, the preferred format specifier should be %u not %d.
> diff --git a/drivers/net/wireless/mediatek/mt7601u/debugfs.c b/drivers/net/wireless/mediatek/mt7601u/debugfs.c
[]
> @@ -88,7 +88,7 @@ mt7601u_eeprom_param_show(struct seq_file *file, void *data)
> dev->ee->rssi_offset[0], dev->ee->rssi_offset[1]);
> seq_printf(file, "Reference temp: %hhx\n", dev->ee->ref_temp);
> seq_printf(file, "LNA gain: %hhx\n", dev->ee->lna_gain);
> - seq_printf(file, "Reg channels: %hhu-%hhu\n", dev->ee->reg.start,
> + seq_printf(file, "Reg channels: %hhu-%d\n", dev->ee->reg.start,
> dev->ee->reg.start + dev->ee->reg.num - 1);
And this is not a promotion of an argument to int via varargs.
The arithmetic did the promotion.
I suggest s/%hh/%/ for all the uses here, not just this one.
checkpatch could do this somewhat automatically.
Of course any changes it suggests need human review.
$ ./scripts/checkpatch.pl -f drivers/net/wireless/mediatek/mt7601u/debugfs.c --show-types --types=unnecessary_modifier --fix-inplace
$ git diff --stat -p drivers/net/wireless/mediatek/mt7601u/debugfs.c
---
drivers/net/wireless/mediatek/mt7601u/debugfs.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/drivers/net/wireless/mediatek/mt7601u/debugfs.c b/drivers/net/wireless/mediatek/mt7601u/debugfs.c
index 20669eacb66ea..b7a6376e3352e 100644
--- a/drivers/net/wireless/mediatek/mt7601u/debugfs.c
+++ b/drivers/net/wireless/mediatek/mt7601u/debugfs.c
@@ -83,28 +83,28 @@ mt7601u_eeprom_param_show(struct seq_file *file, void *data)
struct tssi_data *td = &dev->ee->tssi_data;
int i;
- seq_printf(file, "RF freq offset: %hhx\n", dev->ee->rf_freq_off);
- seq_printf(file, "RSSI offset: %hhx %hhx\n",
+ seq_printf(file, "RF freq offset: %x\n", dev->ee->rf_freq_off);
+ seq_printf(file, "RSSI offset: %x %x\n",
dev->ee->rssi_offset[0], dev->ee->rssi_offset[1]);
- seq_printf(file, "Reference temp: %hhx\n", dev->ee->ref_temp);
- seq_printf(file, "LNA gain: %hhx\n", dev->ee->lna_gain);
- seq_printf(file, "Reg channels: %hhu-%hhu\n", dev->ee->reg.start,
+ seq_printf(file, "Reference temp: %x\n", dev->ee->ref_temp);
+ seq_printf(file, "LNA gain: %x\n", dev->ee->lna_gain);
+ seq_printf(file, "Reg channels: %u-%u\n", dev->ee->reg.start,
dev->ee->reg.start + dev->ee->reg.num - 1);
seq_puts(file, "Per rate power:\n");
for (i = 0; i < 2; i++)
- seq_printf(file, "\t raw:%02hhx bw20:%02hhx bw40:%02hhx\n",
+ seq_printf(file, "\t raw:%02x bw20:%02x bw40:%02x\n",
rp->cck[i].raw, rp->cck[i].bw20, rp->cck[i].bw40);
for (i = 0; i < 4; i++)
- seq_printf(file, "\t raw:%02hhx bw20:%02hhx bw40:%02hhx\n",
+ seq_printf(file, "\t raw:%02x bw20:%02x bw40:%02x\n",
rp->ofdm[i].raw, rp->ofdm[i].bw20, rp->ofdm[i].bw40);
for (i = 0; i < 4; i++)
- seq_printf(file, "\t raw:%02hhx bw20:%02hhx bw40:%02hhx\n",
+ seq_printf(file, "\t raw:%02x bw20:%02x bw40:%02x\n",
rp->ht[i].raw, rp->ht[i].bw20, rp->ht[i].bw40);
seq_puts(file, "Per channel power:\n");
for (i = 0; i < 7; i++)
- seq_printf(file, "\t tx_power ch%u:%02hhx ch%u:%02hhx\n",
+ seq_printf(file, "\t tx_power ch%u:%02x ch%u:%02x\n",
i * 2 + 1, dev->ee->chan_pwr[i * 2],
i * 2 + 2, dev->ee->chan_pwr[i * 2 + 1]);
@@ -112,8 +112,8 @@ mt7601u_eeprom_param_show(struct seq_file *file, void *data)
return 0;
seq_puts(file, "TSSI:\n");
- seq_printf(file, "\t slope:%02hhx\n", td->slope);
- seq_printf(file, "\t offset=%02hhx %02hhx %02hhx\n",
+ seq_printf(file, "\t slope:%02x\n", td->slope);
+ seq_printf(file, "\t offset=%02x %02x %02x\n",
td->offset[0], td->offset[1], td->offset[2]);
seq_printf(file, "\t delta_off:%08x\n", td->tx0_delta_offset);
Justin Stitt <[email protected]> wrote:
> When building with Clang we encounter this warning:
> | drivers/net/wireless/mediatek/mt7601u/debugfs.c:92:6: error: format
> | specifies type 'unsigned char' but the argument has type 'int'
> | [-Werror,-Wformat] dev->ee->reg.start + dev->ee->reg.num - 1);
>
> The format specifier used is `%hhu` which describes a u8. Both
> `dev->ee->reg.start` and `.num` are u8 as well. However, the expression
> as a whole is promoted to an int as you cannot get smaller-than-int from
> addition. Therefore, to fix the warning, use the promoted-to-type's
> format specifier -- in this case `%d`.
>
> example:
> ```
> uint8_t a = 4, b = 7;
> int size = sizeof(a + b - 1);
> printf("%d\n", size);
> // output: 4
> ```
>
> See more:
> (https://wiki.sei.cmu.edu/confluence/display/c/INT02-C.+Understand+integer+conversion+rules)
> "Integer types smaller than int are promoted when an operation is
> performed on them. If all values of the original type can be represented
> as an int, the value of the smaller type is converted to an int;
> otherwise, it is converted to an unsigned int."
>
> Signed-off-by: Justin Stitt <[email protected]>
> Acked-by: Jakub Kicinski <[email protected]>
Patch applied to wireless-next.git, thanks.
68204a696505 wifi: mt7601u: fix clang -Wformat warning
--
https://patchwork.kernel.org/project/linux-wireless/patch/[email protected]/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches